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15 Mar 2005

Volume 97, Issue 6, Articles (06xxxx)

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Atomic ordering-induced band gap reductions in GaAsSb epilayers grown by molecular beam epitaxy

B. P. Gorman, A. G. Norman, R. Lukic-Zrnic, C. L. Littler, H. R. Moutinho, T. D. Golding, and A. G. Birdwell

J. Appl. Phys. 97, 063701 (2005); http://dx.doi.org/10.1063/1.1834983 (7 pages) | Cited 2 times

Online Publication Date: 1 March 2005

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A series of GaAs1−xSbx epilayers (0.51<x<0.71) grown by molecular-beam epitaxy on GaAs substrates with surface orientations of (001), (001) −8° toward (111)A, (001) −8° toward (111)B, (115)A, (115)B, (113)A, and (113)B were investigated using temperature-dependent Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy. Atomic ordering in these epilayers was observed from a decrease in the energy gap measured by FTIR absorption and corroborated by superlattice reflections in electron diffraction. Contrary to previous investigations of ordering in III-V alloys, a marked energy-gap reduction, corresponding to CuPt-B-type ordering, is observed in the GaAs1−xSbx grown on (111)A-type substrate offcuts.
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68.55.-a Thin film structure and morphology
73.20.At Surface states, band structure, electron density of states
78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Fs III-V and II-VI semiconductors
68.37.Lp Transmission electron microscopy (TEM)

Spin detectors operating in the medium-energy range

Henri-Jean Drouhin

J. Appl. Phys. 97, 063702 (2005); http://dx.doi.org/10.1063/1.1852074 (7 pages)

Online Publication Date: 1 March 2005

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Solid-state spin filters consisting of ultrathin ferromagnetic layers can be used as convenient spin polarimeters. A few years ago, a good sensitivity was demonstrated using a Pd/Fe bilayer deposited onto a n-type ozonized GaAs substrate, the spin detector being operated around 800 eV primary energy. From the analysis of the experimental data, a spin-dependent transport scheme is proposed. This provides keys for the practical development of spin filters in the keV range, an energy domain which is well suited for application, and opens perspectives in the study of hot-electron transport in metals.
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75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Np Metals and alloys
73.20.At Surface states, band structure, electron density of states
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Contact mechanisms and design principles for Schottky contacts to group-III nitrides

S. Noor Mohammad

J. Appl. Phys. 97, 063703 (2005); http://dx.doi.org/10.1063/1.1856226 (19 pages) | Cited 20 times

Online Publication Date: 9 March 2005

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Contact mechanisms and design principles for Schottky contacts to group-III nitrides have been studied. These contacts, made generally by using simple principles and past experiences, suffer from serious drawbacks. The importance of various parameters such as surface morphology, surface treatment, metal/semiconductor interactions at the interface, thermal stability, minimization of doping by metal deposition and etching, elimination of edge electric field, etc., for them has been thoroughly investigated. Several design principles have been proposed. Both theoretical and experimental data have been presented to justify the validity of the proposed contact mechanisms and design principles. While theoretical calculations provide fundamental physics underlying heavy doping, leakage, etc., the experimental data provide verification of the contact mechanisms and design principles. The proposed principles are general enough to be applicable to most, if not all, Schottky contacts.
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73.30.+y Surface double layers, Schottky barriers, and work functions
85.30.Hi Surface barrier, boundary, and point contact devices
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.65.Cf Surface cleaning, etching, patterning
73.40.Ns Metal-nonmetal contacts
61.72.uj III-V and II-VI semiconductors
68.60.Dv Thermal stability; thermal effects
61.72.Cc Kinetics of defect formation and annealing
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology

Effects of lattice mismatch and bulk anisotropy on interband tunneling in broken-gap heterostructures

A. Zakharova, S. T. Yen, K. Nilsson, and K. A. Chao

J. Appl. Phys. 97, 063704 (2005); http://dx.doi.org/10.1063/1.1857058 (9 pages) | Cited 2 times

Online Publication Date: 9 March 2005

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We have studied the effects of bulk anisotropy and the strain induced by lattice mismatch on the interband tunneling in broken-gap single-barrier InAs/AlSb/GaSb heterostructures and double-barrier InAs/AlSb/GaSb/InAs/AlSb/GaSb heterostructures. We have used the eight-band k∙p model and the scattering matrix method, combined with the Burt envelope function theory, to calculate the interband transmission coefficients through the broken-gap heterostructures. We have found a noticeable anisotropy of the transmission coefficients when the magnitude of the in-plane wave vector increases to around 0.25 nm−1. We have also found that the strain and the bulk anisotropy of quasiparticle dispersion produce additional peaks in the tunneling probability. For the double-barrier resonant-tunneling structures we discover a large spin splitting of the resonant-tunneling peaks caused by the lack of inversion symmetry. A strong influence of the strain induced by lattice mismatch appears in the current–voltage characteristics of the studied broken-gap heterostructures. In InAs/AlSb/GaSb structures the interband tunneling processes into the heavy-hole states contribute mainly to the peak current density if the sample is grown on InAs, but if the sample is grown on GaSb the interband tunneling processes into the light-hole states become the main contribution to the peak current density. As a result, the structure grown on GaSb has a much larger peak current density. This phenomenon was observed experimentally.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.63.Hs Quantum wells
73.40.Gk Tunneling
73.21.Fg Quantum wells
71.55.Eq III-V semiconductors
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
68.35.Gy Mechanical properties; surface strains

Bulk GaN and AlGaN/GaN heterostructure drift velocity measurements and comparison to theoretical models

J. M. Barker, D. K. Ferry, D. D. Koleske, and R. J. Shul

J. Appl. Phys. 97, 063705 (2005); http://dx.doi.org/10.1063/1.1854724 (5 pages) | Cited 23 times

Online Publication Date: 9 March 2005

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The room-temperature velocity-field characteristics for n-type gallium nitride and AlGaN/GaN heterostructures, grown epitaxially on sapphire, were determined experimentally. A pulsed voltage input and four-point measurements were used on special geometry samples to determine the electron drift velocity as a function of applied electric field in the basal plane. These measurements show apparent saturation velocities near 2.5×107 cm/s at 180 kV/cm for the n-type gallium nitride and 3.1×107 cm/s at 140 kV/cm for the AlGaN/GaN heterostructures. A comparison of these studies shows that the experimental velocities are close to previously published simulations based upon Monte Carlo techniques.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Dn Low-field transport and mobility; piezoresistance
72.80.Ey III-V and II-VI semiconductors

A study of conduction in the transition zone between homologous and ZnO-rich regions in the In2O3–ZnO system

Bhupendra Kumar, Hao Gong, and Raman Akkipeddi

J. Appl. Phys. 97, 063706 (2005); http://dx.doi.org/10.1063/1.1862311 (5 pages) | Cited 28 times

Online Publication Date: 9 March 2005

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Indium zinc oxide thin films were deposited by radio-frequency cosputtering and characterized by x-ray photoelectron spectroscopy (XPS), x-ray diffraction, energy dispersion x-ray spectrometry, Hall-effect measurement, and spectrophotometry techniques. All the films have zinc/(zinc+indium) atomic ratio (define as M ratio) higher than 0.60 and exhibited n-type degenerate semiconductor behavior irrespective of their composition. The conductive films have been observed to have a very wide transmittance window (300–2000 nm). An XPS analysis revealed a diminishing oxygen vacancy contribution to carrier concentration with an increase in the M ratio. However, we observed a gradual decrease in carrier concentration until M ratio of 0.79 and then, a significant rise in carrier concentration for M ratio of 0.84, and this was attributed to the replacement of zinc from its lattice position by indium. The XPS studies also revealed asymmetry in zinc 2p3/2 peak, which might be associated with the structure of this ternary system. The effect of the effective mass on the optical band gap of the films was also observed and discussed further.
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73.61.Le Other inorganic semiconductors
78.66.Li Other semiconductors
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
79.60.Dp Adsorbed layers and thin films
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.50.Dn Low-field transport and mobility; piezoresistance
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.J- Point defects and defect clusters
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Direct evidence of internal Schottky barriers at NiSi2 precipitates in silicon by electron holography

Petr Formanek and Martin Kittler

J. Appl. Phys. 97, 063707 (2005); http://dx.doi.org/10.1063/1.1863432 (5 pages) | Cited 4 times

Online Publication Date: 9 March 2005

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Thin NiSi2 precipitates in n-type Si were analyzed by electron holography. A phase shift of the electron wave was observed around the precipitate and gives direct evidence about the existence of an internal Schottky barrier. The barrier at the interface between the precipitate and the Si matrix, doped with 4×1014 cm−3 phosphorus, was estimated to yield about 90 mV. This value is about five times smaller than the dark barrier. The lowering of the barrier can be explained as a consequence of excess charge carriers generated by the incident electron beam.
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73.30.+y Surface double layers, Schottky barriers, and work functions
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Photovoltaic effects on Franz–Keldysh oscillations in photoreflectance spectra: Application to determination of surface Fermi level and surface recombination velocity in undoped GaAs/n-type GaAs epitaxial layer structures

Hideo Takeuchi, Yoshitaka Kamo, Yoshitsugu Yamamoto, Tomoki Oku, Masahiro Totsuka, and Masaaki Nakayama

J. Appl. Phys. 97, 063708 (2005); http://dx.doi.org/10.1063/1.1861968 (16 pages) | Cited 9 times

Online Publication Date: 14 March 2005

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We demonstrate that the surface Fermi level and surface recombination velocity in undoped GaAs/n-type GaAs (i-GaAs/n-GaAs) epitaxial layer structures can be simultaneously estimated from Franz–Keldysh oscillations (FKOs) in photoreflectance spectra, taking account of the photovoltaic effects. Initially, we performed computational studies on the surface electric fields in i-GaAs/n-GaAs structures under the illumination of a probe beam. The surface electric-field strength is sensitive to the surface Fermi level and surface recombination velocity. We have found that these parameters can be evaluated from the dependence of the surface electric-field strength on the probe-beam power density. Next, we estimated experimentally the surface Fermi level and surface recombination velocity in an as-grown i-GaAs/n-GaAs structure by analyzing the photovoltaic effect on the FKOs. The period of the FKOs increases with a decrease in the probe-beam power density. The surface Fermi level and surface recombination velocity are estimated from the probe-beam power dependence of the surface electric-field strength that is obtained from the analysis of the FKOs. We have also applied the analysis of the photovoltaic effect to the assessment of the GaAs surfaces exposed to the nitridation and the catalytic chemical vapor deposition of SiNx. In addition, we have derived a line-shape function of the FKOs from i-GaAs/n-GaAs structures, which is applicable even to the FKOs influenced by a probe-beam interference phenomenon in a layered structure.
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73.50.Pz Photoconduction and photovoltaic effects
73.20.At Surface states, band structure, electron density of states
78.20.Bh Theory, models, and numerical simulation
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
81.40.Tv Optical and dielectric properties related to treatment conditions

Imaging of oxide charges and contact potential difference fluctuations in atomic layer deposited Al2O3 on Si

J. M. Sturm, A. I. Zinine, H. Wormeester, Bene Poelsema, R. G. Bankras, J. Holleman, and J. Schmitz

J. Appl. Phys. 97, 063709 (2005); http://dx.doi.org/10.1063/1.1870113 (8 pages) | Cited 7 times

Online Publication Date: 14 March 2005

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Ultrathin 2.5 nm high-k aluminum oxide (Al2O3) films on p-type silicon (001) deposited by atomic layer deposition (ALD) were investigated with noncontact atomic force microscopy (NC-AFM) in ultrahigh vacuum, using a conductive tip. Constant force gradient images revealed the presence of oxide charges and experimental observations at different tip–sample potentials were compared with calculations of the electric force gradient based on a spherical tip model. This model could be substantially improved by the incorporation of the image of the tip in the semiconductor substrate. Based on the signals of different oxide charges observed, a homogenous depth distribution of those charges was derived. Application of a potential difference between sample and tip was found to result in a net electric force depending on the contact potential difference (CPD) and effective tip–sample capacitance, which depends on the depletion or accumulation layer that is induced by the bias voltage. CPD images could be constructed from height–voltage spectra with active feedback. Apart from oxide charges large-scale (150–300 nm lateral size) and small-scale (50–100 nm) CPD fluctuations were observed, the latter showing a high degree of correlation with topography features. This correlation might be a result from the surface-inhibited growth mode of the investigated layers.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
73.40.Cg Contact resistance, contact potential
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.37.Ps Atomic force microscopy (AFM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology

Characterization of a silicon–germanium quantum dot structure at 4.2 K and 40 mK

D. S. Gandolfo, D. A. Williams, and H. Qin

J. Appl. Phys. 97, 063710 (2005); http://dx.doi.org/10.1063/1.1862759 (4 pages) | Cited 6 times

Online Publication Date: 14 March 2005

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Characterization of a trench-isolated double quantum dot fabricated from silicon germanium has been carried out via low-temperature electron transport measurements. Coulomb oscillations have been observed, and the mean energy required to add a single electron to the quantum dot was 3.9 meV at 4.2 K and 2.9 meV at 40 mK. The total capacitance of the double-quantum dot increased from 40 aF at 4.2 K to 55 aF at 40 mK.
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73.21.La Quantum dots
73.23.Hk Coulomb blockade; single-electron tunneling
73.63.Kv Quantum dots

Effect of surface localized states on conductivity in an organic crystal

J. Reynaert, K. Poot, V. Arkhipov, G. Borghs, and P. Heremans

J. Appl. Phys. 97, 063711 (2005); http://dx.doi.org/10.1063/1.1866478 (5 pages) | Cited 3 times

Online Publication Date: 14 March 2005

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Current-voltage characteristics of perylene crystals have been measured at different temperatures both with coplanar Au contacts and in the sandwich configuration in between an indium tin oxide bottom contact and a Au top contact. The voltage and temperature dependences of the current turned out to be very different in coplanar and sandwich structures. A strong increase of the conductivity in coplanar contact structures was observed upon oxygen-plasma treatment, indicating a strong influence of surface states on electronic properties of organic crystals. The effect of crystal-growth conditions on electronic parameters of the crystal is discussed. The obtained experimental data are interpreted in terms of dopant-assisted charge injection across a metal-organics interface.
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81.05.Hd Other semiconductors
73.20.At Surface states, band structure, electron density of states
73.40.Ns Metal-nonmetal contacts
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.10.Bk Growth from vapor

Electron wave interferometry through an asymmetric Aharonov–Bohm ring

E. R. Hedin, R. M. Cosby, Y. S. Joe, and A. M. Satanin

J. Appl. Phys. 97, 063712 (2005); http://dx.doi.org/10.1063/1.1858873 (6 pages) | Cited 5 times

Online Publication Date: 15 March 2005

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A nanoscale Aharonov–Bohm (AB) ring functioning as an electron wave interferometer is investigated. The total transmission through the ring is calculated as a function of electron energy and threaded magnetic flux for a fixed upper to lower arm length asymmetry ratio. In addition, we model the effects of an asymmetry in the arm transverse widths by inserting an attractive potential well (dot) in one arm. The combined transmission resonance effects as a function of these variables will be presented. It is shown that an attractive potential in one of the arms in the AB ring generates an asymmetric Fano resonance in the transmission. Our theoretical AB-ring model is compared qualitatively to experimental results from measurements of an asymmetric ring fabricated onto a GaAs/AlGaAs heterostructure, where Fano resonance has been observed.
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85.35.Ds Quantum interference devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.La Quantum dots
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