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November 2009

Volume 106, Issue 10, partial issue

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Surface plasmon resonance-based gas sensor with chalcogenide glass and bimetallic alloy nanoparticle layer

Anuj Sharma
and Rajan Jha

J. Appl. Phys. 106, 103101 (2009) (4 pages)

Online Publication Date: 16 November 2009

Full Text: Read Online | Download PDF (313 KB)

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A theoretical model for a gas sensor based on chalcogenide prism and surface plasmon resonance is proposed. The metal layer consists of Ag–Au alloy nanoparticles. The chalcogenide prism is made of sulfide glass Ge20Ga5Sb10S65, commonly known as 2S2G. The angular interrogation method is used to analyze the sensor’s performance in terms of its intrinsic sensitivity that takes into account both the angular shift as well as the angular width of plasmon resonance curve. The effect of operating wavelength along with the size and composition ratio of alloy nanoparticle is studied on sensor's performance. The sensor’s performance improves with an increase in nanoparticle size and silver fraction. Large operating wavelength is found to be useful for accurate gas sensing. Therefore, proposed sensor can be very useful for gaseous sensing in infrared due to large operating window of chalcogenide materials.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Enhanced response of current-driven coupled quantum wells

Antonios Balassis
and Godfrey Gumbs

J. Appl. Phys. 106, 103102 (2009) (6 pages)

Online Publication Date: 17 November 2009

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We have investigated the conditions necessary to achieve stronger Cherenkov-like instability of plasma waves leading to emission in the terahertz regime for semiconductor quantum wells. The surface response function is calculated for a bilayer two-dimensional electron gas (2DEG) system in the presence of a periodic spatial modulation of the equilibrium electron density. The 2DEG layers are coupled to surface plasmons arising from excitations of free carriers in the bulk region between the layers. A current is passed through one of the layers and is characterized by a drift velocity vD for the driven electric charge. By means of a surface response function formalism, the plasmon dispersion equation is obtained as a function of frequency ω, in-plane wave vector q∥ = (qx,qy), and reciprocal lattice vector nG, where n = 0,±1,±2,… and G = 2π/d, with d denoting the period of the density modulation. The dispersion equation, which yields the resonant frequencies, is solved numerically in the complex ω-plane for the real wave vector q∥. It is ascertained that the imaginary part of ω is enhanced with decreasing d and with increasing doping density of the free carriers in the bulk medium for a fixed period of the spatial modulation.
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73.21.Fg Quantum wells
73.22.Lp Collective excitations
81.07.St Quantum wells

Influence of C60 morphology on high-order harmonic generation enhancement in fullerene-containing plasma

R. Ganeev ,
H. Singhal ,
P. Naik ,
J. Chakera ,
A. Srivastava ,
T. Dhami ,
M. Joshi ,
and P. Gupta

J. Appl. Phys. 106, 103103 (2009) (7 pages)

Online Publication Date: 18 November 2009

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The morphologies of the fullerene targets and the ablated fullerenes to determine the optimal conditions of excitation of the C60-containing targets have been analyzed. The optimization of fullerene-containing plasma conditions allowed the enhanced harmonic generation in these plasmas using laser radiation of different wavelengths, pulse durations, and phase modulation. A comparison between the harmonic generation in single-atom/ion-containing plasmas (using bulk carbon, silver, and indium targets) and fullerene-rich plasma plumes showed better conversion efficiency for the latter medium. The influence of phase modulation of the fundamental radiation in fullerene plasmas on the spectral properties of harmonics has been studied.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
52.38.Mf Laser ablation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
61.48.-c Structure of fullerenes and related hollow and planar molecular structures

Enhancement of light transmission by coupling to surface plasmon polaritons of a layer-plus-islands silver layer

Pangpang Wang ,
Dongyan Zhang ,
Dong Kim ,
Zhiyong Qiu ,
Lumei Gao ,
Ri-ichi Murakami ,
and Xiaoping Song

J. Appl. Phys. 106, 103104 (2009) (5 pages)

Online Publication Date: 18 November 2009

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Enhanced light transmission through coupling incident light with surface plasmon polaritons (SPPs) on a layer-plus-islands nanostructure Ag layer, surrounded by symmetric ZnO dielectrics (ZnO/Ag/ZnO), was investigated. The couple and decouple processes at ZnO/Ag and Ag/ZnO grating interfaces were considered to confine the incident light to SPPs (near field) and then to excite the SPPs to radiate light (far field), which enhanced light transmission. A broad range of light transmission enhancement showed a blueshift with increasing Ag midlayer mass thickness. The physical reasons for light transmission enhancement were theoretically discussed using both the metal/dielectric grating interface model and the Drude–Lorentz free electron model.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
73.22.Lp Collective excitations
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
42.79.Dj Gratings
42.79.Wc Optical coatings
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Spectroscopic investigation of wave driven microwave plasmas

R. Wijtvliet ,
E. Felizardo ,
E. Tatarova ,
F. Dias ,
C. Ferreira ,
S. Nijdam ,
E. Veldhuizen ,
and G. Kroesen

J. Appl. Phys. 106, 103301 (2009) (7 pages)

Online Publication Date: 17 November 2009

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Large H atom line broadening was found throughout the volume of surface wave generated He–H2 and H2 microwave plasmas at low pressures. The measured Doppler temperatures corresponding to the Hβ, Hγ, Hδ, Hε, and Hζ line profiles were found to be higher than the rotational temperature of the hydrogen molecular Fulcher-α band and the Doppler temperature of the 667.1 nm singlet He line. No excessive broadening has been found. The Lorentzian and Gaussian widths as determined by fitting the spectral lines with a Voigt profile increase with the principal quantum number of the upper level. In contrast, no such dependence for the Gaussian width has been observed in an Ar–H2 discharge. No population inversion has been observed from measurements of the relative intensities of transitions within the Balmer series.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.80.Pi High-frequency and RF discharges

Effect of azimuthally asymmetric reactor components on a parallel plate capacitively coupled plasma

Jason Kenney ,
Shahid Rauf ,
and Ken Collins

J. Appl. Phys. 106, 103302 (2009) (6 pages)

Online Publication Date: 19 November 2009

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A three-dimensional fluid plasma model is used to investigate the impact of azimuthally asymmetric reactor components on spatial characteristics of parallel plate capacitively coupled plasmas. We consider three scenarios: high frequency (13.56 MHz) argon discharges with, separately, an off-axis circular plate surrounding the bottom electrode and an access port opening in the reactor sidewall, and a very high frequency (162 MHz) argon discharge with nonparallel electrodes. For the reactor with off-axis plate, both the Ar+ density and flux are strongly perturbed toward the direction of maximum grounded surface area, with azimuthal variation in ion flux up to 10%. Perturbations in Ar+ density due to the access port opening are localized to the region near the access port, and the impact on ion flux in the interelectrode region is minimal. Finally, the nonparallel electrodes result in a significant change in the location and shape of the Ar+ density profile, going from a center-peaked discharge with parallel electrodes to a flattened off-center profile when tilted less than 1° with a nominal 5 cm gap.
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52.80.Pi High-frequency and RF discharges
52.65.-y Plasma simulation

Degradation of Staphylococcus aureus bacteria by neutral oxygen atoms

U. Cvelbar ,
M. Mozetic ,
N. Hauptman ,
and M. Klanjšek-Gunde

J. Appl. Phys. 106, 103303 (2009) (5 pages)

Online Publication Date: 19 November 2009

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The degradation of Staphylococcus aureus bacteria during treatment with neutral oxygen atoms was monitored by scanning electron microscopy. Experiments were performed in an afterglow chamber made from borosilicate glass. The source of oxygen atoms was remote inductively coupled radiofrequency oxygen plasma. The density of atoms at the samples was 8×1020 m−3. The treatment was performed at room temperature. The first effect was the removal of dried capsule. Capsule on exposed parts of bacteria was removed after receiving the dose of 6×1023 at./m2, while the parts of capsule filling the gaps between bacteria were removed after receiving the dose of 2.4×1024 m−2. After removing the capsule, degradation continued as etching of bacterial cell wall. The etching was rather nonuniform as holes with diameter of several 10 nm were observed. The cell wall was removed after receiving the dose of about 7×1024 m−2. The etching probabilities were about 2×10−5 for the capsule and 2×10−6 for the cell wall. The results were explained by different compositions of capsule and the cell wall.
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87.50.sj Dosimetry/exposure assessment
52.50.Dg Plasma sources
87.80.-y Biophysical techniques (research methods)
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Extended x-ray absorption fine structure study of arsenic in HgCdTe: p-type doping linked to nonsubstitutional As incorporation in an unknown AsHg8 structure

X. Biquard ,
I. Alliot ,
and P. Ballet

J. Appl. Phys. 106, 103501 (2009) (8 pages)

Online Publication Date: 16 November 2009

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An extended x-ray absorption fine structure (EXAFS) investigation has been carried out on arsenic-doped Hg70Cd30Te samples. The incorporation of atomic arsenic has been achieved using a nonconventional radio-frequency plasma source in a molecular beam epitaxy reactor. Two samples from the same epitaxial wafer have been studied. One underwent a 400 °C activation annealing under Hg pressure, leading to n to p-type conversion. In the commonly admitted scenario, this conversion is associated with the annealing-induced migration of As from a Hg site to a Te site. This study shows that this is not the case. Before annealing, As is found to be involved in noncrystalline structures: 50% inside an As2Te3 chalcogenide glass and 50% inside a new AsHg8 compact structure. After annealing, the As2Te3 chalcogenide glass disappears, 31% of As occupies Hg sites and 69% incorporates inside this new AsHg8 compact structure that occupies Te sites. The EXAFS results are in excellent agreement with 77 K Hall-effect measurements. The new AsHg8 structure is found to have an acceptor behavior. Overall, this study provides an entirely new vision of extrinsic p-type doping of HgCdTe as well as the first experimental evidence of As site transfer induced by annealing.
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78.70.Dm X-ray absorption spectra
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Ga II-VI semiconductors
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
61.72.uj III-V and II-VI semiconductors
81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

In situ x-ray diffraction investigation on early stages of oxidation at 900 °C of γ-TiAl dipped in a phosphoric acid solution

S. Brou ,
P. Renault ,
C. Huvier ,
J. Grosseau-Poussard ,
and G. Bonnet

J. Appl. Phys. 106, 103502 (2009) (6 pages)

Online Publication Date: 16 November 2009

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The short term oxidation behavior of γ-TiAl treated in low-concentration phosphoric acid solution has been investigated at 900 °C in air. A pyrophosphate film isomorphous to TiP2O7 is formed during the initial thermal treatment step and is responsible for a subsequent large reduction in the oxidation rate. During the initial course of oxidation at 900 °C, the pyrophosphate film transforms into a TiO2 solid solution containing phosphorus. This transformation impedes the usual oxides external growing mechanisms and leads to an internal development of the oxide scale with an associated reduced oxidation rate.
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81.65.Mq Oxidation
89.40.Dd Air transporation
81.40.Gh Other heat and thermomechanical treatments

Near coalescent submicron polycrystalline diamond films deposited on silicon: Hydrogen bonding and thermal enhanced carbide formation

A. Stacey ,
Sh. Michaelson ,
J. Orwa ,
S. Rubanov ,
S. Prawer ,
B. Cowie ,
and A. Hoffman

J. Appl. Phys. 106, 103503 (2009) (8 pages)

Online Publication Date: 16 November 2009

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The influence of high temperature annealing up to 1200 °C in vacuum on ∼ 100 nm nearly continuous thick diamond films consisting of 30–50 nm crystallites, deposited onto silicon substrates is reported. The hydrogen bonding and phase composition of the films were studied with Raman spectroscopy, while the surface microstructure and composition were studied with high resolution scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS), respectively. Annealing to 800–900 °C of ∼ 100 nm thick films results in a decrease in the intensities of the peaks associated with hydrogen bonding (Raman), as well as changes to the morphological microstructure at the film surface. Heating the films to 1000 °C resulted in the complete disappearance of the Raman peaks associated with hydrogen bonding at grain boundaries, and an increase in the relative intensity of the diamond peak relative to the graphite-related D and G Raman peaks, concomitant with changes to the microstructure (SEM and TEM). Ex situ XP analysis of the films annealed to 800 and 1000 °C provides clear evidence for the formation of SiC on the films surface and near surface region. However a sharp SiC Raman peak at 796 cm−1 appears only after annealing to 1200 °C and it is concomitant with a decrease in the Raman peaks associated with sp2 bonded carbon. Our results suggest that formation of SiC phase preferentially consumes sp2/sp hybridized carbon matrix, produced by thermal desorption of hydrogen atoms at diamond grain boundary and at the diamond film—silicon substrate interface.
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78.66.Nk Insulators
68.47.Fg Semiconductor surfaces
78.30.Hv Other nonmetallic inorganics
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
68.35.Dv Composition, segregation; defects and impurities

A quality map of transfer printing

Matthew Tucker ,
D. Hines ,
and Teng Li

J. Appl. Phys. 106, 103504 (2009) (8 pages)

Online Publication Date: 17 November 2009

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Transfer printing is a nanofabrication technique that involves an assembly process by which a printable layer can be transferred from a transfer substrate to a device substrate. Future application of transfer printing toward a roll-to-roll printing process of flexible devices hinges upon the understanding on the mechanisms governing transfer printing quality, which is far from mature. So far, the quality control of transfer printing has been mainly explored via massive experimental trials, which are both time consuming and cost prohibitive. In this paper, we conduct systematic computational modeling to investigate the governing mechanisms of the transfer printing process. While the existing understanding of transfer printing mainly relies on the differential interfacial adhesion, our results suggest that both interfacial defects (e.g., cracks) and differential interfacial adhesion play pivotal roles in the transfer printing quality. The outcomes of this study define a quality map of transfer printing in the space spanned by the critical mechanical properties and geometrical parameters in a transfer printing structure. Such a quality map offers new insights and quantitative guidance for material selection and design strategies to achieve successful transfer printing.
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81.16.-c Methods of micro- and nanofabrication and processing

Light absorption in silicon quantum dots embedded in silica

S. Mirabella ,
R. Agosta ,
G. Franzò ,
I. Crupi ,
M. Miritello ,
R. Lo Savio ,
M. Di Stefano ,
S. Di Marco ,
F. Simone ,
and A. Terrasi

J. Appl. Phys. 106, 103505 (2009) (8 pages)

Online Publication Date: 17 November 2009

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The photon absorption in Si quantum dots (QDs) embedded in SiO2 has been systematically investigated by varying several parameters of the QD synthesis. Plasma-enhanced chemical vapor deposition (PECVD) or magnetron cosputtering (MS) have been used to deposit, upon quartz substrates, single layer, or multilayer structures of Si-rich-SiO2 (SRO) with different Si content (43–46 at. %). SRO samples have been annealed for 1 h in the 450–1250 °C range and characterized by optical absorption measurements, photoluminescence analysis, Rutherford backscattering spectrometry and x-ray Photoelectron Spectroscopy. After annealing up to 900 °C SRO films grown by MS show a higher absorption coefficient and a lower optical bandgap ( ∼ 2.0 eV) in comparison with that of PECVD samples, due to the lower density of Si–Si bonds and to the presence of nitrogen in PECVD materials. By increasing the Si content a reduction in the optical bandgap has been recorded, pointing out the role of Si–Si bonds density in the absorption process in small amorphous Si QDs. Both the photon absorption probability and energy threshold in amorphous Si QDs are higher than in bulk amorphous Si, evidencing a quantum confinement effect. For temperatures higher than 900 °C both the materials show an increase in the optical bandgap due to the amorphous-crystalline transition of the Si QDs. Fixed the SRO stoichiometry, no difference in the optical bandgap trend of multilayer or single layer structures is evidenced. These data can be profitably used to better implement Si QDs for future PV technologies.
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78.67.Hc Quantum dots
79.60.Jv Interfaces; heterostructures; nanostructures
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.Cd Deposition by sputtering
78.55.Et II-VI semiconductors
81.07.Ta Quantum dots

Large radiation fields from nonlocal interaction between terahertz waves and quantum wells with an applied electric field

Guanghui Wang
and Qi Guo

J. Appl. Phys. 106, 103506 (2009) (6 pages)

Online Publication Date: 17 November 2009

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The effects of pump intensities and applied electric fields on radiation fields excited by the nonlocal interaction between terahertz waves and AlGaAs/GaAs quantum wells (QWs) are investigated. The numerical results show the resonant radiation fields are very large in the confinement direction, and their spectra and spatial distributions are tunable by the applied electric field. In addition, it is clarified that the second-order and third-order nonlinearities will emerge when the pump intensity reaches 108 and 109 W/m2 orders of magnitude, respectively, and the latter makes the second-harmonic (SH) intensity derivate from the expected square law dependence on the pump intensity, even induces the system into saturation. The maximum SH conversion efficiency is 4.3×10−4. These results are helpful for the accurate observations on the nonlinear optical effects in the QWs by experiment.
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78.67.De Quantum wells
78.66.Fd III-V semiconductors
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.20.Jq Electro-optical effects

Strength of lithium fluoride under shockless compression to 114 GPa

T. Ao ,
M. Knudson ,
J. Asay ,
and J.-P. Davis

J. Appl. Phys. 106, 103507 (2009) (12 pages)

Online Publication Date: 18 November 2009

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A magnetic loading technique was used to ramp load single-crystal [100] lithium fluoride specimens to peak stresses of 5–114 GPa. Wave analysis of in situ particle velocity profiles was used to estimate the compressive strength of LiF at peak stress. It was found that the strength increased with peak stress and showed two distinct regions of hardening; the first is believed to be governed by strain hardening and the second by pressure hardening. The quasielastic strain obtained from the initial part of the unloading was shown to saturate at about 1.3% for peak stresses greater than approximately 30 GPa. Over the studied pressure range, the measured strength of LiF varied from its initial value of 0.08 to about 1.1 GPa at the highest compressed state of 114 GPa. Comparison of the measured strength to results from two strength models showed good agreement. It was demonstrated that the strength of LiF introduces systematic error of about 10% when used as an interferometer window for measurements of material strength in isentropic compression experiments.
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62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Energy transfer rates and population inversion of math11/2 excited state of Er3+ investigated by means of numerical solutions of the rate equations system in Er:LiYF4 crystal

Laércio Gomes ,
André Librantz ,
Fabio Jagosich ,
Wonder Alves ,
Izilda Ranieri ,
and Sonia Baldochi

J. Appl. Phys. 106, 103508 (2009) (9 pages)

Online Publication Date: 18 November 2009

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In this work, we present the spectroscopic properties of LiYF4 (YLF) single crystals activated by high doping of erbium ions. The most important processes that lead to the up-conversion erbium emissions in the infrared region were identified. A time-resolved luminescence spectroscopy technique was employed to measure the luminescence decays and to determine the most important mechanisms involved in the up-conversion processes that populate the math3/2 excited state. A study of the energy transfer up-conversion (ETU) processes in Er:YLF showed that an ETU rate can be obtained from the math11/2 (ETU1) and math3/2 (ETU2) up-conversion luminescence transient analysis, i.e., from best fittings of the acceptor state luminescence. An analysis of the ETU rate dependence on the wavelength and intensity of pulsed laser excitations allowed us to obtain the ETU rate constants from the lower (math13/2) and upper (math11/2) laser levels to use them in the numerical solutions of the rate equation system for the Er-doped YLF crystal (15 mol %) pumped [continuous wave (cw)] at 972 nm. As a result, we found that the math11/2→math13/2 laser emission (or small signal gain) shows a temporal profile intensity, which passes through a maximum at around 820 μs before getting the steady state regime. It was demonstrated that the ETU2 process (from the math11/2 level) is the mechanism responsible for the laser gain profile observed. The results of the numerical simulation of the rate equation system showed that the highest population inversion density of 8.5×1019 cm−3 for Er3+ (or a small signal gain of 2.54 cm−1) is obtained for 15 mol % of erbium in the YLF crystal when it is pumped by a cw laser at 972 nm using a pump intensity of 5.4 kW cm−2 (or a pumping rate of 300 s−1) for the laser transition near 2.75 μm. It was seen also that a pumping rate of 300 s−1 maximizes the population inversion in the cw pump regime. A simulation using a square wave pump with a pumping time of 1 ms showed a population inversion increasing by a factor of 1.31 with respect to the population inversion obtained in the continuous pump simulation.
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78.30.Hv Other nonmetallic inorganics
61.72.up Other materials
78.47.jd Time resolved luminescence
78.55.Hx Other solid inorganic materials
42.62.Fi Laser spectroscopy

Ge–Sb–Te thin films deposited by pulsed laser: An ellipsometry and Raman scattering spectroscopy study

P. Němec ,
A. Moreac ,
V. Nazabal ,
M. Pavlišta ,
J. Přikryl ,
and M. Frumar

J. Appl. Phys. 106, 103509 (2009) (7 pages)

Online Publication Date: 18 November 2009

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Pulsed laser (532 nm) deposited Ge2Sb2Te5 thin films were investigated by means of spectroscopic ellipsometry and Raman scattering spectroscopy. Tauc–Lorentz and Cody–Lorentz models were employed for the evaluation of optical functions of thin films in as-deposited (amorphous) and crystalline (cubic) phases. The models’ parameters (Lorentz oscillator amplitude, resonance energy, oscillator width, optical band gap, and Urbach energy) calculated for amorphous and crystalline states are discussed. The vibrational modes observed in Raman spectra of amorphous layers are attributed to GeTe4−nGen (n = 1, 2, eventually 0) tetrahedra connected by corners (partly by edges) and SbTe3 units. The Raman spectra of crystalline thin films suggest that the local bonding arrangement around Ge atoms changes; GeTe component is thus mainly responsible for the phase transition in Ge2Sb2Te5 alloys.
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78.66.Jg Amorphous semiconductors; glasses
81.15.Fg Pulsed laser ablation deposition
68.55.ag Semiconductors
61.43.Dq Amorphous semiconductors, metals, and alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics

Extension of the Rosencwaig–Gersho–Fernelius photothermal deflection spectroscopy model to account for multiple reflections in epitaxial samples

I. Chan
and M. Beaudoin

J. Appl. Phys. 106, 103510 (2009) (8 pages)

Online Publication Date: 19 November 2009

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The Fernelius extension to the Rosencwaig–Gersho theory for photothermal deflection spectroscopy (PDS) is modified to take into account multiple reflections and light trapping within a thin film-on-substrate system where both the thin film and the substrate can be absorbing. The extended model is used to simulate the PDS signal from bulk GaAs and GaNAs epilayers grown on GaAs substrates. While the PDS magnitude signal shows a strong dependence on the light trapping effects, the phase signal remains almost insensitive to this effect. However, the PDS relative phase is very sensitive to the sample thickness.
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68.55.ag Semiconductors
68.35.bg Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Thermal stability and vibrational spectroscopy of N–O shallow donor centers in silicon

Hans Alt
and Hans Wagner

J. Appl. Phys. 106, 103511 (2009) (9 pages)

Online Publication Date: 20 November 2009

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N–O-related shallow donors in nitrogen-doped Czochralski silicon have been studied by infrared spectroscopy. Quasithermal equilibrium states were established by long-term thermal annealing in the temperature range from 600 to 1000 °C. By quantitative analysis of the 1s→2p± far-infrared electronic transitions between 230 and 250 cm−1, it is found that the formation and decay characteristics of these centers do not correspond to theoretical predictions. All complexes investigated show a monotonic decrease for annealing temperatures above 600 °C. In particular, the dominant NO2 complex exhibits a pronounced biexponential decay behavior. Based on the characteristic thermal fingerprint of the individual shallow donor species, associated local vibrational modes in the midinfrared were investigated. Two bands at 1070 and 860 cm−1 can be assigned to NO2, the center with the highest concentration variation in the relevant temperature range between 600 and 800 °C. These frequencies match favorably with recent calculations for this complex in the symmetrical O–N–O configuration.
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78.30.Hv Other nonmetallic inorganics
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
71.55.Cn Elemental semiconductors
81.05.Cy Elemental semiconductors
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling

Optical spectroscopy and upconversion luminescence in Nd3+ doped Ga10Ge25S65 glass

Vineet Rai ,
Cid de Araújo ,
Y. Ledemi ,
B. Bureau ,
M. Poulain ,
and Y. Messaddeq

J. Appl. Phys. 106, 103512 (2009) (5 pages)

Online Publication Date: 20 November 2009

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Optical properties of a neodymium (Nd3+) doped glass having composition based on the (Ga2S3)–(GeS2) system are reported. Transition probabilities, radiative lifetimes, and branching ratios related to Nd3+ levels were determined. Frequency upconversion (UC) luminescence due to nonresonant excitation at 1064 nm was observed at ≈ 535, ≈ 600, and ≈ 670 nm. The dependence of the UC intensity on the laser intensity and on the Nd3+ concentration as well as the dynamics of the luminescence process were studied. The results indicate that two-photon absorption by isolated Nd3+ ions and energy transfer among pairs of Nd3+ ions contribute to the UC luminescence.
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78.55.Hx Other solid inorganic materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Photoinduced spin-polarized current in InSb-based structures

M. Frazier ,
J. Cates ,
J. Waugh ,
J. Heremans ,
M. Santos ,
X. Liu ,
and G. Khodaparast

J. Appl. Phys. 106, 103513 (2009) (5 pages)

Online Publication Date: 20 November 2009

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We demonstrate the observation of spin-polarized photocurrent in InSb films grown on GaAs and InP substrates and InSb quantum wells where a nonequilibrium spin population has been achieved by using circularly polarized radiation. The characteristics of our observations indicated that the circular photo galvanic effect could be responsible for the generation of the photocurrents.
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73.61.Ey III-V semiconductors
73.63.Hs Quantum wells
72.25.Dc Spin polarized transport in semiconductors
72.40.+w Photoconduction and photovoltaic effects

Enhancement of phosphorus activation in vacancy engineered thin silicon-on-insulator substrates

A. Smith ,
R. Gwilliam ,
V. Stolojan ,
A. Knights ,
P. Coleman ,
A. Kallis ,
and S. Yeong

J. Appl. Phys. 106, 103514 (2009) (5 pages)

Online Publication Date: 20 November 2009

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The concentration of vacancy-type defects in a silicon-on-insulator substrate consisting of a 110 nm silicon overlayer and a 200 nm buried oxide has been quantified using variable energy positron annihilation spectroscopy following 300 keV Si+ ion implantation to a dose of 1.5×1015 cm−2 and subsequent annealing at temperatures ranging from 300 to 700 °C. The preferential creation of vacancies (relative to interstitials) in the silicon overlayer leads to a net vacancy-type defect concentration after annealing. Assuming that the defects have a structure close to that of the divacancy we determine the concentration to range from 1.7×1019 to 5×1018 cm−3 for annealing temperatures ranging from 300 to 700 °C. The measured defect concentration is in excellent agreement with that predicted via Monte Carlo simulation. The impact of this net vacancy population on the diffusion and activation of phosphorus introduced by a 2 keV implantation to a dose of 1×1015 cm−2 has been observed. For samples that combine both Si+ and P+ implantations, postimplantation phosphorus diffusion is markedly decreased relative to that for P+ implantation only. Further, a fourfold increase in the electrical activation of phosphorus after postimplantation annealing at 750 °C is observed when both implantations of Si+ and P+ are performed. We ascribe this affect to the reduction in phosphorus-interstitial clusters by the excess vacancy concentration beyond the amorphous/crystalline interface created by the P+ implantation.
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61.72.uf Ge and Si
61.72.sd Impurity concentration
61.72.jd Vacancies
61.72.jj Interstitials
61.80.Fe Electron and positron radiation effects
61.72.Cc Kinetics of defect formation and annealing
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Effect of annealing on charge transfer in Ge nanocrystal based nonvolatile memory structure

M. Yang ,
T. Chen ,
Z. Liu ,
J. Wong ,
W. Zhang ,
S. Zhang ,
and Y. Liu

J. Appl. Phys. 106, 103701 (2009) (7 pages)

Online Publication Date: 16 November 2009

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Ge nanocrystals (nc-Ge) embedded in the gate oxide of the nonvolatile memory structure were synthesized by Ge ion implantation followed by thermal annealing at 800 °C for various durations. Large changes in the structural and chemical properties of the Ge+-implanted oxide have been observed, and they have been found to possess a significant impact on the charge transfer in the oxide layer. The distribution and concentration of the nc-Ge and dissolved Ge atoms which serve as both the charge storage and transfer sites in the oxide are affected by the annealing. Two charge transfer mechanisms, i.e., the lateral charge diffusion along the Ge-distributed layer and the charge leakage from the charge storage sites to the Si substrate via the charge transfer sites, have been identified based on the charge retention behaviors. Both mechanisms are enhanced by the annealing as a result of the change in the distribution and concentration of the charge transfer sites.
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61.72.Cc Kinetics of defect formation and annealing
61.46.-w Structure of nanoscale materials
85.30.Kk Junction diodes
61.72.uf Ge and Si
66.30.H- Self-diffusion and ionic conduction in nonmetals

Energy relaxation probed by weak antilocalization measurements in GaN heterostructures

H. Cheng ,
N. Biyikli ,
J. Xie ,
Ç. Kurdak ,
and H. Morkoç

J. Appl. Phys. 106, 103702 (2009) (4 pages)

Online Publication Date: 16 November 2009

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Energy relaxation and electron-phonon (e-p) interaction are investigated in wurtzite Al0.15Ga0.85N/AlN/GaN and Al0.83In0.17N/AlN/GaN heterostructures with polarization induced two-dimensional electron gases in the Bloch–Grüneisen regime. Weak antilocalization (WAL) and Shubnikov–de Haas measurements were performed on gated Hall bar structures at temperatures down to 0.3 K. We used WAL as a thermometer to measure the electron temperature Te as a function of the dc bias current. We found that the power dissipated per electron, Pe, was proportional to Te4 due to piezoelectric acoustic phonon emission by hot electrons. We calculated Pe as a function of Te without any adjustable parameters for both the static and the dynamic screening cases of piezoelectric e-p coupling. In the temperature range of this experiment, the static screening case was expected to be applicable; however, our data was in better agreement with the dynamic screening case.
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73.20.Fz Weak or Anderson localization
63.20.kd Phonon-electron interactions
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
77.65.-j Piezoelectricity and electromechanical effects
72.80.Ey III-V and II-VI semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions

Enhanced thermoelectric performance by the combination of alloying and doping in TiCoSb-based half-Heusler compounds

Pengfei Qiu ,
Xiangyang Huang ,
Xihong Chen ,
and Lidong Chen

J. Appl. Phys. 106, 103703 (2009) (6 pages)

Online Publication Date: 16 November 2009

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TiCoSb-based half-Heusler compounds have been prepared and their thermoelectric properties are studied. By isoelectronic alloying on the Ti site with Zr, although both the thermal conductivity and electrical conductivity are suppressed, the Seebeck coefficient is improved remarkably with a highest value of −420 μV/K for Ti0.5Zr0.5CoSb at 600 K, which provides a larger space to optimize the thermoelectric performance. To further improve the performance of the TiCoSb-based isoelectronic alloy, doping Ni on the Co site was explored. It is found that small amount of Ni doping results in a great increase in the electrical conductivity, still with a relative large Seebeck coefficient. Ti0.6Hf0.4Co0.87Ni0.13Sb sample exhibits a peak power factor of 23.4 μW/cm K2, which is the highest value for n-type TiCoSb-based half-Heusler compounds reported so far. As a result, a maximum dimensionless figure of merit of 0.70 has been achieved at 900 K for Ti0.6Hf0.4Co0.87Ni0.13Sb.
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72.15.Jf Thermoelectric and thermomagnetic effects
61.72.up Other materials

Arsenic antisite defects in p-GaAs grown by metal-organic chemical-vapor deposition and the EL2 defect

Nazir Naz ,
Umar Qurashi ,
and M. Iqbal

J. Appl. Phys. 106, 103704 (2009) (7 pages)

Online Publication Date: 17 November 2009

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Epitaxial layers of p-GaAs grown on p+-GaAs substrates by low-pressure metal organic chemical vapor deposition have been investigated using deep level transient spectroscopy (DLTS). One dominant peak and other relatively small peak, corresponding to deep levels at Ev+0.55 eV and Ev+0.96 (low field energies), respectively, have been observed in the lower half of the band gap. Investigation with double-correlation DLTS reveals that the measured thermal emission rate of holes from the dominant level is strongly dependent on the junction electric field. Detailed data on this field enhancement have been analyzed in terms of different available theoretical models. The hole capture cross section for the dominant deep level has been found to be temperature dependent. Detailed data on the temperature dependence of the hole capture cross section have been interpreted in terms of the multiphonon carrier capture mechanism, yielding a capture barrier of 0.11 eV. In order to get deeper insight into the nature and origin of these inadvertent (intrinsic) defects, thermal annealing behavior of these levels has also been studied. Analyses of field dependence and hole capture data, in combination with the annealing study, suggest that the dominant level is associated with an arsenic-antisite (AsGa) defect. Probable association of this dominant level with the doubly charged state of the well-known EL2 defect has been discussed in detail.
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81.05.Ea III-V semiconductors
68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
71.55.Eq III-V semiconductors
71.20.Nr Semiconductor compounds
63.20.kg Phonon-phonon interactions

Persistent photocurrent and decay studies in CdS nanorods thin films

Gouri Paul
and Pratima Agarwal

J. Appl. Phys. 106, 103705 (2009) (5 pages)

Online Publication Date: 17 November 2009

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Structural and electrical transport properties of thin films of CdS nanorods synthesized by solvothermal process are studied through x-ray diffraction, scanning electron microscopy, transmission electron microscopy, activation energy measurements, and decay of photoconductivity. The films show thermally activated conductivity, high photosensitivity, and persistent photoconductivity, which decays initially fast followed by slow decay. The decay time constant for fast decay are of the order of a few seconds, whereas for slow decay it is in the range of about 100 s. The electrical transport is similar to that in the polycrystalline material. The slow decay of excess conductivity has been attributed to the presence of defects and local potential fluctuations within the nanorods.
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73.61.Ga II-VI semiconductors
73.63.Bd Nanocrystalline materials
73.50.Pz Photoconduction and photovoltaic effects
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Monte Carlo simulation of charge transport in amorphous chalcogenides

Fabrizio Buscemi ,
Enrico Piccinini ,
Rossella Brunetti ,
Massimo Rudan ,
and Carlo Jacoboni

J. Appl. Phys. 106, 103706 (2009) (6 pages)

Online Publication Date: 17 November 2009

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The most peculiar feature exhibited by the I(V) characteristics of amorphous-chalcogenide materials is undoubtedly its S-shaped behavior. This type of characteristics is very important for the technological application, e.g., in the field of nanoscale solid-state memories. In this paper we give a microscopic particle description of the charge transport across a layer of amorphous Ge2Sb2Te5 sandwiched between two planar metallic contacts. A transport scheme based on the generalization of the variable-range hopping has been implemented in a current-driven Monte Carlo code. This approach allows one to investigate the aspects of the microscopic picture responsible for the electrical properties of the device. The results are compared with experimental data.
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73.40.Ns Metal-nonmetal contacts
72.20.Ee Mobility edges; hopping transport
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Jc Amorphous semiconductors; glasses
61.43.Bn Structural modeling: serial-addition models, computer simulation

An impedance spectroscopic investigation of the electrical properties of δ-doped diamond structures

Niall Tumilty ,
Joseph Welch ,
Richard Lang ,
Christopher Wort ,
Richard Balmer ,
and Richard Jackman

J. Appl. Phys. 106, 103707 (2009) (7 pages)

Online Publication Date: 17 November 2009

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Impedance spectroscopy has been used to investigate the conductivity displayed by diamond doped with boron in an intrinsic-δ-layer-intrinsic multilayer system with differing δ-layer thicknesses. Carrier transport within 5 nm δ-layer structures is complex, being dominated by conduction in the interfacial regions between the δ-layer and the intrinsic regions, as well as conduction within the δ-layer itself. In the case of 3.2 nm thick δ-layers the situation appears improved with uncapped samples supporting only two conduction paths, one of which may be associated with transport outside of the δ-layer, the other low transport within the δ-layer complex diamond structures. Introduction of the capping layer creates a third conduction path associated with unwanted boron in the capping layer-δ-layer interface.
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81.05.ug Diamond
61.72.up Other materials
72.80.Cw Elemental semiconductors
72.20.Ee Mobility edges; hopping transport
81.05.Cy Elemental semiconductors

Alpha particle detection with GaN Schottky diodes

A. Polyakov ,
N. Smirnov ,
A. Govorkov ,
A. Markov ,
E. Kozhukhova ,
I. Gazizov ,
N. Kolin ,
D. Merkurisov ,
V. Boiko ,
A. Korulin ,
V. Zalyetin ,
S. Pearton ,
I.-H. Lee ,
A. Dabiran ,
and P. Chow

J. Appl. Phys. 106, 103708 (2009) (5 pages)

Online Publication Date: 17 November 2009

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Ni/GaN Schottky diode radiation detectors were fabricated on 3-μm-thick unintentionally doped n-GaN films grown by molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) and on 12-μm-thick undoped n-GaN layers prepared by epitaxial lateral overgrowth (ELOG). The reverse current of all detector structures was <10−9 A for bias voltages necessary for detector operation, with the level of background donor doping of <1015 cm−3. With this doping level the space charge region of the Schottky diode could be extended to the entire thickness of the films. The charge collection efficiency of the detectors was close to 100% for MOCVD and ELOG detectors for α-particles with range comparable to the thickness of the layer. Electrical properties and deep trap spectra were also studied. The collection efficiency decreased when the concentra-tion of deep electron traps, particularly Ec-0.6 eV traps, increased in MBE grown films.
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29.40.-n Radiation detectors
85.30.Kk Junction diodes

Highly mismatched crystalline and amorphous GaN1−xAsx alloys in the whole composition range

K. Yu ,
S. Novikov ,
R. Broesler ,
I. Demchenko ,
J. Denlinger ,
Z. Liliental-Weber ,
F. Luckert ,
R. Martin ,
W. Walukiewicz ,
and C. Foxon

J. Appl. Phys. 106, 103709 (2009) (8 pages)

Online Publication Date: 18 November 2009

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Alloying is a commonly accepted method to tailor properties of semiconductor materials for specific applications. Only a limited number of semiconductor alloys can be easily synthesized in the full composition range. Such alloys are, in general, formed of component elements that are well matched in terms of ionicity, atom size, and electronegativity. In contrast there is a broad class of potential semiconductor alloys formed of component materials with distinctly different properties. In most instances these mismatched alloys are immiscible under standard growth conditions. Here we report on the properties of GaN1−xAsx, a highly mismatched, immiscible alloy system that was successfully synthesized in the whole composition range using a nonequilibrium low temperature molecular beam epitaxy technique. The alloys are amorphous in the composition range of 0.17<x<0.75 and crystalline outside this region. The amorphous films have smooth morphology, homogeneous composition, and sharp, well defined optical absorption edges. The band gap energy varies in a broad energy range from ∼ 3.4 eV in GaN to ∼ 0.8 eV at x ∼ 0.85. The reduction in the band gap can be attributed primarily to the downward movement of the conduction band for alloys with x>0.2, and to the upward movement of the valence band for alloys with x<0.2. The unique features of the band structure offer an opportunity of using GaN1−xAsx alloys for various types of solar power conversion devices.
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81.05.Gc Amorphous semiconductors
68.55.ag Semiconductors
61.43.Dq Amorphous semiconductors, metals, and alloys
71.20.Nr Semiconductor compounds

Metal-semiconductor transition in epitaxial ZnO thin films

M. Nistor ,
F. Gherendi ,
N. Mandache ,
C. Hebert ,
J. Perrière ,
and W. Seiler

J. Appl. Phys. 106, 103710 (2009) (7 pages)

Online Publication Date: 20 November 2009

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We report on the formation and transport properties of ZnO thin films which are grown by pulsed-electron beam deposition under a low residual oxygen pressure (10−5 mbar). ZnO films presenting metallic conductivity at room temperature, and a metal-semiconductor transition at low temperature, were epitaxially grown on