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1 Dec 1999

Volume 86, Issue 11, pp. 5927-6612

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Lorentzian noise in the two-dimensional electron gas of AlxGa1−xAs/GaAs quantum wells

Yuping Chen, Carolyne M. Van Vliet, Paul M. Koenraad, and Grover L. Larkins

J. Appl. Phys. 86, 6206 (1999); http://dx.doi.org/10.1063/1.371732 (7 pages) | Cited 2 times

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Current noise spectra SI(ω) are reported on samples grown by the molecular beam epitaxy technique, with current-carrying contacts, acting as source and drain, and two probes extending into the two-dimensional electron gas (2DEG) of the AlGaAs/GaAs quantum well, in the range 77–295 K for frequencies of 10 Hz to 1 MHz. The time constants are almost independent of temperature and the current dependence is close to linear. The noise is interpreted as Lorentzian-modulated shot noise of the 2DEG current. © 1999 American Institute of Physics.
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73.50.Td Noise processes and phenomena
73.61.Ey III-V semiconductors

Preparation and thermoelectric properties of some phosphide skutterudite compounds

A. Watcharapasorn, R. C. DeMattei, R. S. Feigelson, T. Caillat, A. Borshchevsky, G. J. Snyder, and J.-P. Fleurial

J. Appl. Phys. 86, 6213 (1999); http://dx.doi.org/10.1063/1.371635 (5 pages) | Cited 19 times

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Thermoelectric properties of CoP3 and CeFe4P12 have been measured. These compounds were synthesized by a flux technique using Sn as the solvent. The samples were characterized by x-ray diffractometry and electron microprobe analyses. The Seebeck coefficient, the electrical resistivity, the Hall effect, and the thermal conductivity were measured over a wide range of temperatures. The results indicate that CoP3 and CeFe4P12 are semiconductors, in agreement with theoretical predictions. The thermal conductivity of CeFe4P12 is about 10 times larger than that for CeFe4Sb12 which is primarily due to both reduced motion of the Ce ions in smaller voids and lower hole–phonon scattering. The results are analyzed and discussed to provide guidelines for optimization of the thermoelectric properties of these materials. © 1999 American Institute of Physics.
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72.80.Ga Transition-metal compounds
72.20.Pa Thermoelectric and thermomagnetic effects
72.20.My Galvanomagnetic and other magnetotransport effects
81.05.Hd Other semiconductors
81.10.Dn Growth from solutions
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Generalized analysis of quasi-steady-state and quasi-transient measurements of carrier lifetimes in semiconductors

Henning Nagel, Christopher Berge, and Armin G. Aberle

J. Appl. Phys. 86, 6218 (1999); http://dx.doi.org/10.1063/1.371633 (4 pages) | Cited 75 times

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Recently, a simple yet powerful carrier lifetime technique for semiconductor wafers has been introduced that is based on the simultaneous measurement of the light-induced photoconductance of the sample and the corresponding light intensity [Appl. Phys. Lett. 69, 2510 (1996)]. In combination with a light pulse from a flash lamp, this method allows the injection level dependent determination of the effective carrier lifetime in the quasi-steady-state mode as well as the quasi-transient mode. For both cases, approximate solutions (those for steady-state and transient conditions) of the underlying semiconductor equations have been used. However, depending on the actual lifetime value and the time dependence of the flash lamp, specific systematic errors in the effective carrier lifetime arise from the involved approximations. In this work, we present a generalized analysis that avoids these approximations and hence substantially extends the applicability of the quasi-steady-state and quasi-transient methods beyond their previous limits. © 1999 American Institute of Physics.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects

Photoacoustic determination of the recombination velocity at the AlGaAs/GaAs heterostructure interface

I. Reich, P. Díaz, T. Prutskij, J. Mendoza, H. Vargas, and E. Marín

J. Appl. Phys. 86, 6222 (1999); http://dx.doi.org/10.1063/1.371676 (8 pages) | Cited 11 times

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The surface recombination velocity at the AlGaAs/GaAs single heterostructure interface is determined using the photoacoustic technique. We analyze different heat generation mechanisms for this type of heterostructure with different Al composition and thickness of the AlGaAs layers. A theoretical model of the photoacoustic signal generation in the heat transmission detection configuration was developed. The values of the surface recombination velocity obtained by comparing the theoretical expressions with the experimental results are in good agreement with the literature reported ones. The results were also correlated with those of photoluminescence measurements in the same samples. © 1999 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.25.+i Surface conductivity and carrier phenomena
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

Monte Carlo simulation of electron transport in 2H-SiC using a three valley analytical conduction band model

H-E. Nilsson and M. Hjelm

J. Appl. Phys. 86, 6230 (1999); http://dx.doi.org/10.1063/1.371677 (4 pages) | Cited 10 times

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A Monte Carlo study of the electron transport in 2H-SiC is presented. The study is based on a three valley analytical band model that has been derived from an ab initio band structure calculation. The scattering models have been extrapolated from recent Monte Carlo simulations of 4H-SiC and 6H-SiC. The low field mobility in the c-axis direction is higher than in 4H-SiC and 6H-SiC, while the mobility perpendicular to the c axis is similar. The saturation velocity at 300 K obtained from the Monte Carlo simulation is 2.3×107 cm/s for field applied in the c-axis direction and 1.9×107 cm/s for field applied perpendicular to the c-axis direction. The difference in mean energy as a function of electric field between 2H-SiC and 4H-SiC or 6H-SiC is large. The energy spectrum along the c axis in 2H-SiC is not discontinuous as in the case of 4H-SiC and 6H-SiC, which gives 2H-SiC a higher mean energy for electric fields applied in the c-axis direction. This indicates that the electron impact ionization coefficients should be higher for 2H-SiC. © 1999 American Institute of Physics.
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72.80.Jc Other crystalline inorganic semiconductors
71.20.Nr Semiconductor compounds
72.20.Ht High-field and nonlinear effects
71.15.-m Methods of electronic structure calculations
72.20.Fr Low-field transport and mobility; piezoresistance

Relaxation of positive charge during bidirectional electric stress on metal–oxide–silicon capacitors

A. El-Hdiy and Dj Ziane

J. Appl. Phys. 86, 6234 (1999); http://dx.doi.org/10.1063/1.371719 (5 pages) | Cited 8 times

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Relaxation phenomena of positive charges, created in a metal–oxide–silicon capacitor by bidirectional Fowler–Nordheim electron injections under constant current, have been studied and their kinetics have been quantitatively characterized. After creation, positive charges are neutralized under electron injections at constant current. The gate bias shift caused by the neutralization process has an exponential dependence on time during relaxation irrespective of stress field polarity and stress duration. Analysis of data assuming nonelectron detrapping gives capture cross section values in the range of 3.5–6.7×10−16 to 2.1×10−15 cm2. The compilation of data given in literature and our present results shows that the main responsible defect in the oxide is the amphoteric traps negatively charged near the cathode and positively charged near the anode. © 1999 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Spin-polarized tunneling in a half-metallic ferromagnet

Clifford T. Tanaka, Janusz Nowak, and Jagadeesh S. Moodera

J. Appl. Phys. 86, 6239 (1999); http://dx.doi.org/10.1063/1.371678 (4 pages) | Cited 74 times

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Direct measurement of the conduction electron spin polarization (P) in epitaxial NiMnSb was performed to test the prediction of half metallicity in this material. Spin-polarized tunneling in NiMnSb/Al2O3/Al junctions showed P of 28%, contrary to the predicted value of 100%. Magnetoresistance measurements in NiMnSb/Al2O3/Ni80Fe20 junctions concurred with this result. The discrepancy between theory and experiment is discussed. Also, the latter junctions show four nonvolatile remanent states due to the NiMnSb magnetocrystalline anisotropy, which has potential as four-level logic elements. © 1999 American Institute of Physics.
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73.40.Rw Metal-insulator-metal structures
73.40.Gk Tunneling
75.45.+j Macroscopic quantum phenomena in magnetic systems
72.15.Gd Galvanomagnetic and other magnetotransport effects
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Magnetoresistance in low-temperature grown molecular-beam epitaxial GaAs

J. Betko, M. Morvic, J. Novák, A. Förster, and P. Kordoš

J. Appl. Phys. 86, 6243 (1999); http://dx.doi.org/10.1063/1.371679 (6 pages) | Cited 4 times

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Conductivity, Hall effect as well as “physical” and “geometrical” magnetoresistances were measured at 290–440 K in molecular-beam epitaxial GaAs layers grown at 200–400 °C. The experimental data were analyzed taking into account the combined band and hopping conductance regime. Positive hopping magnetoresistance parameters (Δρ/ρ0B2)h ≈ 10−4 T−2 and hopping Hall mobilities lower than 1×10−4 m2 V−1 s−1 were determined in the as-grown layers. A transverse-to-longitudinal hopping magnetoresistance ratio of about 2, consistent with hopping transport theories, was obtained. In the annealed layer grown at 200 °C (J200a) the band mobility determined from the geometrical magnetoresitance (GMR) mobility was found to be significantly higher than the band Hall mobility. It is related to a mixed band conductivity regime with the hole concentration p exceeding the electron one n. The difference between GMR and Hall mobilities decreases with increasing growth temperature as far as a typical single-carrier band conductivity regime (n>p) is present in the layer grown at 400 °C. In contradiction to the layers grown at higher temperatures, the J200a layer showed the opposite (positive) sign of the hopping Hall coefficient as well as the largest hopping magnetoresistance parameter ( ≈ 3×10−2 T−2). © 1999 American Institute of Physics.  
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73.61.Ey III-V semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Numerical simulation of electron diffraction through a narrow constriction

Akira Endoh, Shigehiko Sasa, Hiroshi Arimoto, and Shunichi Muto

J. Appl. Phys. 86, 6249 (1999); http://dx.doi.org/10.1063/1.371680 (7 pages) | Cited 2 times

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We performed time-evolved numerical simulations of a two-dimensional electron wave packet passing through a semicircular constriction (very short quantum wire) by solving the time-dependent Schrödinger equation using the finite difference method to understand the nature of electron diffraction phenomena in semiconductors. By Fourier transformation, we calculated the time-evolved electron wave packet in wave number space, which shows the transition from the Gaussian distribution to the circular distribution having equal energy by entering constriction. The obtained results are compared with the results of our previous simulations of an electron wave packet passing through a rectangular constriction. By analyzing the nature of diffracted subpeaks, the following results were obtained: (1) The intensity of the subpeaks diffracted by a semicircular constriction is higher than that by a rectangular one. (2) The starting point of the diffracted subpeaks is the center position of the narrowest width in a constriction, while that for rectangular ones is the center of the constriction entrance. (3) The lateral wave number of the diffracted subpeak increases with the number n, n being the number counted from the main (0th) peak which propagates straight through, although it deviates negatively from the linear relationship obtained for rectangular ones with an increase in n. (4) There is a time delay in the diffracted subpeaks similar to that for rectangular constrictions. The differences between passing through a semicircular constriction and a rectangular one were interpreted as caused by the reflection on the inside wall of the constriction and the energy spread of each quantum level. © 1999 American Institute of Physics.
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61.05.jd Theories of electron diffraction and scattering
03.65.Ge Solutions of wave equations: bound states

Temperature dependence of the E2 and A1(LO) phonons in GaN and AlN

A. Link, K. Bitzer, W. Limmer, R. Sauer, C. Kirchner, V. Schwegler, M. Kamp, D. G. Ebling, and K. W. Benz

J. Appl. Phys. 86, 6256 (1999); http://dx.doi.org/10.1063/1.371681 (5 pages) | Cited 45 times

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The frequencies and dampings of the zone-center optical phonons E2 and A1(LO) in wurtzite-type GaN and AlN layers have been measured by Raman spectroscopy in the temperature range from 85 to 760 K. The GaN layer was grown by metalorganic vapor phase epitaxy and the AlN layer by molecular beam epitaxy both on sapphire substrate. The experimentally obtained frequencies and dampings are modeled by a theory taking into account the thermal expansion of the lattice, a symmetric decay of the optical phonons into two and three phonons of lower energy, and the strain in the layers induced by the different thermal expansion coefficients of layer and substrate. The results were used to determine the local temperature of a GaN pn diode in dependence on the applied voltage. © 1999 American Institute of Physics.
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63.20.-e Phonons in crystal lattices
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
65.40.De Thermal expansion; thermomechanical effects

Barrier height enhancement of Ag/n-GaAs and Ag/n-InP Schottky diodes prepared by P2S5/(NH4)2Sx and HF treatments

Ming-Jer Jeng, Hung-Tsung Wang, Liann-Be Chang, Yi-Chang Cheng, and Shu-Tsun Chou

J. Appl. Phys. 86, 6261 (1999); http://dx.doi.org/10.1063/1.371682 (3 pages) | Cited 7 times

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A method for surface passivation using both the phosphorus sulfide/ammonia sulfide [P2S5/(NH4)2Sx] solution and hydrogen fluoride (HF) solution has shown great effectiveness on the barrier height enhancement of Ag/n-GaAs and Ag/n-InP Schottky diodes. It is found that, even though the Ag/n-GaAs and Ag/n-InP diodes were baked for 18 h at 300 °C, their Schottky barriers could still reach as high as 1.1 and 0.95 eV, respectively. After the bare semiconductor substrates were bathed successively in P2S5/(NH4)2Sx and HF solutions and then shone by an ultraviolet light, the analysis with x-ray photoelectron spectroscopy indicates a possible formation of ultrathin and stable sulfur fluoride or phosphorus fluoride layers on the substrate surfaces. The formation of these stable interface layers has been attributed to the enhancement of Schottky barrier heights. © 1999 American Institute of Physics.
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85.30.Hi Surface barrier, boundary, and point contact devices
85.30.Kk Junction diodes
81.65.Rv Passivation
81.05.Ea III-V semiconductors

Electroluminescence and photoelectric properties of type II broken-gap n-In(Ga)As(Sb)/N-GaSb heterostructures

K. D. Moiseev, M. P. Mikhailova, N. D. Stoyanov, Yu. P. Yakovlev, E. Hulicius, T. Simecek, J. Oswald, and J. Pangrác

J. Appl. Phys. 86, 6264 (1999); http://dx.doi.org/10.1063/1.371683 (5 pages) | Cited 5 times

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Layers of n-InAs and n-InGaAsSb were grown by metalorganic vapor phase epitaxy and liquid phase epitaxy on N-GaSb substrates. The electroluminescence, current-voltage characteristics and photocurrent spectra of these heterostructures were studied at low temperatures. It was shown that GaSb/In(Ga)As(Sb) with InAs-rich narrow-gap solid solutions are broken-gap heterojunctions of type II at 77 and 300 K. Intense electroluminescence of the N-GaSb/n-In(Ga)As(Sb) heterostructures was found in the spectral range of 3–4 μm at 77 K. The origin of radiative recombination at the N-n type II broken-gap heterointerface is proposed and is in agreement with the experimental results for both systems. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
78.60.Fi Electroluminescence
73.50.Pz Photoconduction and photovoltaic effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Electron mobility in extremely thin single-gate silicon-on-insulator inversion layers

F. Gámiz, J. B. Roldán, P. Cartujo-Cassinello, J. E. Carceller, J. A. López-Villanueva, and S. Rodriguez

J. Appl. Phys. 86, 6269 (1999); http://dx.doi.org/10.1063/1.371684 (7 pages) | Cited 20 times

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Inversion-layer mobility has been investigated in extremely thin silicon-on-insulator metal–oxide–semiconductor field-effect transistors with a silicon film thickness as low as 5 nm. The Poisson and Schrœdinger equations have been self-consistently solved to take into account inversion layer quantization. To evaluate the electron mobility, the Boltzmann transport equation has been solved by the Monte Carlo method, simultaneously taking into account phonon, surface-roughness, and Coulomb scattering. We show that the reduction of the silicon layer has several effects on the electron mobility: (i) a greater confinement of the electrons in the thin silicon film, which implies an increase in the phonon-scattering rate and therefore a mobility decrease; (ii) a reduction in the conduction effective mass and the intervalley-scattering rate due to the redistribution of carriers in the two subband ladders as a consequence of size quantization resulting in a mobility increase; and (iii) an increase in Coulomb scattering because of a greater number of interface traps in the buried Si–SiO2 and to a closer approach of these charged centers to the mobile carriers. The dependence of these effects on the silicon-layer thickness and on the inversion-charge concentration causes the mobility to be a nontrivial function of these variables. A detailed explanation of the mobility behavior is provided. Mobility for samples with silicon thickness below 10 nm is shown to increase in an electric field range that depends on the charged center concentration, while for silicon layers over 10 nm mobility always decreases as the silicon-layer thickness is reduced. © 1999 American Institute of Physics.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.De Semiconductor-device characterization, design, and modeling
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Bk General theory, scattering mechanisms
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