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15 Dec 1994

Volume 76, Issue 12, pp. 7671-8220

Page 2 of 4 Pages Previous Page Next Page | Jump to Page

A local vibrational mode investigation of p‐type Si‐doped GaAs

M. J. Ashwin, M. R. Fahy, R. C. Newman, J. Wagner, D. A. Robbie, M. J. L. Sangster, I. Silier, E. Bauser, W. Braun, and K. Ploog

J. Appl. Phys. 76, 7839 (1994); http://dx.doi.org/10.1063/1.357892 (11 pages) | Cited 6 times

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Infrared absorption (IR) and Raman scattering measurements have been made of the localized vibration modes (LVM) due to defects incorporating silicon impurities in p‐type Si‐doped GaAs grown by liquid phase epitaxy (LPE) on (001) planes and by molecular beam epitaxy (MBE) on (111)A and (311)A planes. Analysis of a closely compensated LPE sample indicated that an existing calibration factor for the SiAs LVM (399 cm−1) relating the integrated absorption coefficient (IA) to the concentration [SiAs] should be increased by 40%, so that IA=1 cm−2 corresponds to [SiAs]=7×1016 cm−3. The SiAs LVM appeared as a Fano dip in the hole absorption continuum at ∼395 cm−1 in the highly doped p‐type material, some 4 cm−1 lower in frequency than its normal position in compensated GaAs. Electron irradiation of samples led to the progressive removal of the Fano dip and a shift with the emergence of the expected SiAs LVM absorption line at 399 cm−1. In MBE samples the irradiation also generated SiGa donors, but the site switching was not detected in LPE material. By contrast, Raman spectra of as‐grown p‐type samples exhibited a symmetrical peak at 395 cm−1, which also shifted towards 399 cm−1 as the free carriers were removed. MBE (111)A GaAs:Si compensated by SnGa donors revealed the SiAs LVM at its normal position. After hydrogenation of MBE and LPE samples, only stretch modes due to H‐SiAs were observed. Passivated MBE GaAs (111)A codoped with Si and Be showed stretch modes due to both shallow acceptors. It was thereby concluded that only one type of acceptor (SiAs) was present in p‐type Si‐doped GaAs, contrary to previous proposals. There was no evidence for the presence of SiAs pairs or larger clusters. © 1994 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
63.20.Pw Localized modes
78.30.Fs III-V and II-VI semiconductors

Intermetallic phase formation during annealing of Al/Ni multilayers

A. S. Edelstein, R. K. Everett, G. Y. Richardson, S. B. Qadri, E. I. Altman, J. C. Foley, and J. H. Perepezko

J. Appl. Phys. 76, 7850 (1994); http://dx.doi.org/10.1063/1.357893 (10 pages) | Cited 44 times

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The phase evolution during annealing of Al/Ni multilayer samples prepared by ion‐beam sputtering with composition modulation wavelengths Λ between 10 and 400 nm was determined using x‐ray diffraction and differential scanning calorimeter measurements. Samples with average compositions of Al0.40Ni0.60 and Al0.75Ni0.25 were investigated. For the Al0.40Ni0.60 samples the following results were obtained. A measure of the degree of periodicity and the sharpness of the interfaces in a sample with Λ=80 nm was the large number (over 20) of peaks observed in small‐angle x‐ray scattering measurements. A sample with Λ=10 nm was transformed by heat treatment directly to the AlNi phase. In the Λ=80 nm sample, the first phase formed after annealing was the metastable η phase. The η phase was identified as Al9Ni2. In the 400 nm wavelength sample, both the metastable η phase and the stable Al3Ni formed after the first exothermic reaction. For the Al0.75Ni0.25 samples two results were obtained. A Λ=11.4 nm sample transformed directly on annealing into Al3Ni. The η phase was the first phase formed on annealing a Λ=100 nm sample. The difference in the component diffusivities and the concentration gradient play an important role in controlling phase formation and evolution. © 1994 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
68.35.Fx Diffusion; interface formation

Surface‐sensitive x‐ray fluorescence analysis at glancing incident and takeoff angles

Kouichi Tsuji, Shigeo Sato, and Kichinosuke Hirokawa

J. Appl. Phys. 76, 7860 (1994); http://dx.doi.org/10.1063/1.357894 (4 pages) | Cited 11 times

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The possibility of the glancing incidence and takeoff x‐ray fluorescence (GIT‐XRF) method for surface analysis has been investigated. In this method the observation depth can be restricted by both the incident angle of primary x rays and the takeoff angle of observed fluorescent x rays. As a result, it has been found that the surface‐sensitive analysis is achieved when the incident angle is small below the critical angle for total reflection of the primary x rays and the takeoff angle is set slightly below the critical angle for total reflection of the fluorescent x rays from the element on the substrate. © 1994 American Institute of Physics.
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78.70.En X-ray emission spectra and fluorescence
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Local structure of CuInSe2 thin film studied by extended x‐ray absorption fine structure

Yuji Kuwahara, Hiroyuki Oyanagi, Hirotaka Yamaguchi, Masakazu Aono, Sho Shirakata, and Shigehiro Isomura

J. Appl. Phys. 76, 7864 (1994); http://dx.doi.org/10.1063/1.357895 (6 pages) | Cited 7 times

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The local structure of CuInSe2 thin films has been studied by extended x‐ray absorption fine structure on the Cu K and Se K edges using synchrotron radiation. The Cu—Se and In—Se bond lengths are examined as a function of In/Cu ratio α (0.29<α<1.13). The results show that the local structure of the thin‐film CuInSe2 is quite similar to that of the bulk crystal over a wide range of α; however, it is found that with decreasing α, the Cu—Se and In—Se bond lengths deviate systematically from those of the stoichiometric bulk CuInSe2 crystal, which is attributed to the chemical disorder of the cation sites and the formation of anion vacancies in the chalcopyrite lattice. The temperature dependencies of mean‐square relative displacements indicate that the In—Se bond is stronger than the Cu—Se bond. © 1994 American Institute of Physics.  
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68.55.-a Thin film structure and morphology
61.05.cf X-ray scattering (including small-angle scattering)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.

Nonlinear optical response, screening, and distribution of strain in piezoelectric multiple quantum wells

X. R. Huang, D. R. Harken, A. N. Cartwright, D. S. McCallum, Arthur L. Smirl, J. L. Sánchez‐Rojas, A. Sacedón, F. González‐Sanz, E. Calleja, and E. Muñoz

J. Appl. Phys. 76, 7870 (1994); http://dx.doi.org/10.1063/1.357896 (4 pages) | Cited 6 times

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By embedding piezoelectric InGaAs/GaAs multiple quantum wells (MQWs) in specifically designed p‐i‐n structures, we demonstrate that the nonlinear optical response can be used to identify the dominant screening mechanisms and simultaneously to determine the strain distribution. Furthermore, we show that a knowledge of the screening mechanisms and spatial band structure, in turn, can be used to control the nonlinear optical response. For this demonstration, we fabricate two p‐i(MQW)‐n samples on [111]‐oriented GaAs substrates. The samples are designed such that, if the dominant screening is associated with photogenerated carriers that remain in the wells, a blue shift of the exciton would be expected in each. By contrast, if the screening is associated with carriers that have escaped the wells and moved to screen the entire MQW, one will shift to the blue and the other to the red if the lattice is mechanically clamped, but both will shift to the red if the lattice is mechanically free. The observation of a blue shift and a red shift indicates that, while in‐well screening may be present, the dominant screening is out‐of‐well and that these particular structures are mechanically clamped to the lattice constant of the GaAs. Most importantly, these results illustrate the added flexibility that the piezoelectric field gives in tailoring the nonlinear optical response. © 1994 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Study of C49‐TiSi2 and C54‐TiSi2 formation on doped polycrystalline silicon using in situ resistance measurements during annealing

L. A. Clevenger, R. W. Mann, R. A. Roy, K. L. Saenger, C. Cabral, and J. Piccirillo

J. Appl. Phys. 76, 7874 (1994); http://dx.doi.org/10.1063/1.357897 (8 pages) | Cited 29 times

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In situ resistance versus temperature or time for reactions between 32 and 57.5 nm of titanium and undoped or doped polycrystalline silicon (boron, arsenic, or phosphorus, 7.9×1019–3.0×1020/cm3) has been measured and no clear correlation was found between the activation energy for the formation of the industrially important low‐resistance C54‐TiSi2 phase and its formation temperature. It is also demonstrated that with certain moderate doping levels typical of complementary metal‐oxide‐semiconductor manufacturing, boron or phosphorus‐doped polycrystalline silicon can delay the formation of C54‐TiSi2 more than arsenic‐doped polycrystalline silicon. Finally, by using in situ resistance measurements, it is demonstrated that the ‘‘two‐step’’ thermal annealing process similar to a salicide process requires less thermal annealing time at high temperatures to form C54‐TiSi2 than a single ‘‘one‐step’’ thermal anneal at the same temperature. © 1994 American Institute of Physics.
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68.55.Nq Composition and phase identification
68.60.Dv Thermal stability; thermal effects
64.70.K- Solid-solid transitions

Hydrogen effect on the optical activity of dislocations in silicon introduced at room temperature

T. Sekiguchi, V. V. Kveder, and K. Sumino

J. Appl. Phys. 76, 7882 (1994); http://dx.doi.org/10.1063/1.357898 (7 pages) | Cited 21 times

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Dislocations were introduced into silicon crystals by mechanical scratching at room temperature. The optical property of such dislocations was investigated by means of cathodoluminescence. Neither deformation‐induced luminescence nor the exciton luminescence was detected in the scratched region, showing that a high density of nonradiative recombination centers is induced on or around dislocations. Hydrogen plasma treatment of a scratched crystal led to the appearance of the so‐called D1–D4 luminescence lines along the scratch. Deep‐level transient spectroscopy revealed that deep traps were induced by scratching and diminished drastically due to subsequent hydrogen plasma treatment. Thus, it was concluded that hydrogen passivated nonradiative recombination centers but not the luminescence centers. The characteristics in spatial distribution of D1 and D2 lines and those of D3 and D4 lines showed that these two groups of luminescence lines were of different origins. Since the specimens used were thought to be free from metal contamination, the luminescence was not related to metallic impurities incorporated in the dislocation core. The nonradiative recombination centers induced by scratching were annihilated due to annealing at temperatures higher than 500 °C. The release of hydrogen from the nonradiative centers in a hydrogenated specimen did not take place before they were annihilated by annealing. © 1994 American Institute of Physics.
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61.72.Lk Linear defects: dislocations, disclinations
71.55.Cn Elemental semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence

Iterative spectral solution of the Poisson‐Boltzmann equation in semiconductor devices

Brian H. Floyd and Yannick L. Le Coz

J. Appl. Phys. 76, 7889 (1994); http://dx.doi.org/10.1063/1.357899 (10 pages) | Cited 4 times

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We present an iterative spectral method for solving the coupled Poisson–Boltzmann equation in semiconductor devices. Both theory and preliminary numerical results, in one spatial dimension (three phase‐space dimensions), are reviewed. The method relies on a multidimensional Hermite–Gaussian‐product expansion of the carrier distribution function’s velocity dependence. Pseudotemporal and spatial variables are discretized using finite differences. Stability of the resulting numerical spectral equations is achieved using an added pseudoviscous term. The present formulation allows full inclusion of realistic phonon‐scattering probability rates by means of a ‘‘collision matrix.’’ Numerical solutions have been obtained for a variety of one‐dimensional semiconductor diode problems. These include ballistic, collisional, equilibrium, and nonequilibrium cases. Comparison, where possible, with analytical solutions has confirmed the validity and accuracy of this spectral approach. © 1994 American Institute of Physics.
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72.10.Bg General formulation of transport theory
85.30.De Semiconductor-device characterization, design, and modeling
02.60.Nm Integral and integrodifferential equations

Thermoelectric properties of Cu‐doped dysprosium sesquisulfide

S. H. Han, K. A. Gschneidner, and B. A. Cook

J. Appl. Phys. 76, 7899 (1994); http://dx.doi.org/10.1063/1.357900 (8 pages) | Cited 2 times

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The electrical resistivity, thermoelectric power (Seebeck coefficient), Hall effect, and thermal conductivity have been measured in Cux(Dy2S3)1−x compounds with the η‐orthorhombic structure in the composition range 0.006≤x≤0.15 in order to determine their potential as high temperature (300–1000 °C) thermoelectric materials. In this temperature and composition range Cu‐doped Dy2S3 behaves as a degenerate semiconductor and shows itinerant conduction. The electrical resistivity and the Seebeck coefficient increased with increasing temperature and reach a maximum value of 4.35–7.13 mΩ cm and −163 to −177 μV/°C, respectively, depending upon the Cu concentration. A maximum power factor of 7.9 μW/cm °C2 for the Cu0.039(Dy2S3)0.961 alloy was observed at 690 °C. The 300–1000 °C integrated average power factor shows that the optimum Cu‐doping level in the Dy2S3 matrix is 5–7 at. %. The thermal conductivity of Cu0.039(Dy2S3)0.961 decreased with increasing temperature from 300 to 1000 °C and was governed by both electronic and lattice contributions up to 600 °C, but above 600 °C the electronic contribution is predominant. The 300–1000 °C integrated average thermal conductivity of Cu0.039(Dy2S3)0.961 is 18.38 mW/cm °C, which gives this material a maximum figure of merit Z of 0.440×10−3/°C at 800 °C. © 1994 American Institute of Physics.
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72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
72.20.Pa Thermoelectric and thermomagnetic effects

Built‐in biaxial strain dependence of Γ‐X transport in GaAs/InxAl1−xAs/GaAs pseudomorphic heterojunction barriers (x=0, 0.03, and 0.06)

K. Yang, J. R. East, G. I. Haddad, T. J. Drummond, T. M. Brennan, and B. E. Hammons

J. Appl. Phys. 76, 7907 (1994); http://dx.doi.org/10.1063/1.357901 (8 pages)

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The effects of built‐in biaxial strain on Γ‐X transport in n‐GaAs/i‐InxAl1−xAs/n‐GaAs pseudomorphic single‐barrier structures (x=0, 0.03, and 0.06) are studied by measuring temperature‐dependent I‐V characteristics. For the accurate characterization of electron transport across each barrier, a self‐consistent numerical model is used to analyze the experimental results. For each structure, the four barrier parameters defined from the thermionic‐field‐emission theory, the effective Richardson constant A∗, the conduction‐band offsets ΔEc1,2, and a tunneling mass mn∗ are extracted by calculating the theoretical I‐V characteristics and fitting them to the experimental I‐V‐T data. The experimentally obtained X‐point conduction‐band shifts with the addition of indium are compared with the theoretical results calculated based on the model‐solid theory. The results indicate that the addition of indium not only splits the degenerate X minima of the InxAl1−xAs barrier, but also shifts the relative barrier heights of both longitudinal and transverse X valleys due to the alloy‐dependent band‐structure modification. The comparison between the experimental and theoretical results illustrates that the transverse X valleys are the main conduction channel for the Γ‐X transport across InxAl1−xAs pseudomorphic barriers. © 1994 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors

Anisotropic dc conductivity in stretch‐oriented iodine‐doped poly[3‐(4‐octylphenyl)‐2,2′‐bithiophene]

P. Dyreklev and O. Inganäs

J. Appl. Phys. 76, 7915 (1994); http://dx.doi.org/10.1063/1.358427 (5 pages) | Cited 2 times

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A square four‐point probe is constructed to measure anisotropic conductivity of small samples. The method is applied to measurements of the anisotropic conductivity of a conjugated polymer. The polymer poly[3‐(4‐octylphenyl)‐2,2′‐bithiophene] is stretch oriented to various elongations and doped with I2 vapor. The conductivity anisotropy is dependent on the degree of orientation and the absolute conductivity. An anisotropy value of 2.4 is obtained for an elongation of four times. For a given elongation the conductivity anisotropy decreases during the spontaneous undoping. The experimental results are discussed in terms of varying charge hopping distances. © 1994 American Institute of Physics.  
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72.80.Le Polymers; organic compounds (including organic semiconductors)
73.61.Ph Polymers; organic compounds

Departures from the principle of superposition in silicon solar cells

S. J. Robinson, A. G. Aberle, and M. A. Green

J. Appl. Phys. 76, 7920 (1994); http://dx.doi.org/10.1063/1.357902 (11 pages) | Cited 10 times

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The principle of superposition forms the theoretical basis on which the comparison of illuminated and dark current‐voltage (I‐V) characteristics of solar cells depends. Two cases predicted from computer simulations where the superposition principle does not apply in silicon p‐n junction solar cells are reported. These predictions are confirmed experimentally with measurements taken on existing high‐efficiency devices, and cannot be accurately described by previous explanations for departures from this principle. The first case, which is the more important in terms of operation under 1 sun illumination, occurs in cells where recombination via defect levels (Shockley–Read–Hall recombination) with unequal electron and hole capture rates dominates the I‐V characteristics. The second case is evident at small forward voltages in almost all silicon solar cells. It is shown that the former is due to a saturation in the recombination rate, while the latter is the result of a bias‐dependent modification of the carrier concentrations across the p‐n junction depletion region which is different under illumination from that in the dark. © 1994 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
84.60.Jt Photoelectric conversion
85.30.De Semiconductor-device characterization, design, and modeling

Schottky barrier height modification on n‐ and p‐type GaInP with thin interfacial Si

T. J. Miller, G. B. Backes, and M. I. Nathan

J. Appl. Phys. 76, 7931 (1994); http://dx.doi.org/10.1063/1.357903 (4 pages) | Cited 6 times

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Al/n:GaInP and Al/p:GaInP Schottky diodes have been grown by molecular‐beam epitaxy with and without thin (6 Å) interfacial Si layers. The Schottky barrier heights were measured by C‐V, I‐V, and I‐V‐T techniques. The n‐ and p‐type barrier heights for the samples without interfacial Si were 0.86 and 0.93 eV, respectively. Interfacial Si enhanced the n‐type barrier by 0.17 eV, and reduced the p‐type barrier by 0.08 eV. The sum of the n‐ and p‐type barrier heights for the samples with the Si layer was equal to the band gap of GaInP; without Si the sum was less. By comparing this data to the Al/Si/GaAs data, GaAs‐GaInP conduction‐ and valence‐band discontinuities of 0.05 and −0.41 eV, respectively, have been inferred. © 1994 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Generation of electron carriers in insulating thin film of MgIn2O4 spinel by Li+ implantation

H. Kawazoe, N. Ueda, H. Un’no, T. Omata, H. Hosono, and H. Tanoue

J. Appl. Phys. 76, 7935 (1994); http://dx.doi.org/10.1063/1.357904 (7 pages) | Cited 38 times

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Li+ implantation at room temperature of insulating thin films of polycrystalline MgIn2O4 spinel (∼1.3 μm thick) was found to generate electron carriers efficiently. Li+ ions were implanted at 80 keV to a fluence of 1×1016 cm−2 and subsequently at 160 keV to the same fluence. Some implanted films were subjected to a post‐annealing at 300 °C. Depth profiles of implanted Li+ ions measured with secondary‐ion‐mass spectroscopy agreed with that calculated with the trim code. Conductivity at room temperature increased from σ<10−7 to ∼101 S cm−1 upon the Li+ implantation. The generation yield of electron carriers in the as‐implanted film was ∼20% and increased up to ∼40% upon post‐annealing. Two optical‐absorption bands were induced upon the implantation, one at about ∼500 nm and another above ∼1000 nm extending to the IR region, which was attributed to plasma oscillation of electron carriers. The former band faded and the latter absorption increased its intensity upon post‐annealing. He+ implantation, which was done for comparison, induced no change in electrical conductivity and no absorption band above ∼1000 nm. © 1994 American Institute of Physics.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ng Insulators
61.72.up Other materials

Investigation of tensile‐strained InGaAlP multiquantum‐well active regions by photoluminescence measurements

Minoru Watanabe, Hatsumi Matsuura, and Naohiro Shimada

J. Appl. Phys. 76, 7942 (1994); http://dx.doi.org/10.1063/1.357905 (5 pages) | Cited 3 times

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The use of a tensile‐strained multiquantum‐well (MQW) active region in 630‐nm‐band InGaAlP MQW laser diodes is investigated through photoluminescence (PL) measurements. The critical conditions for lattice relaxation of strained MQW layers are also discussed. Emissions due to electron–heavy‐hole recombination and electron–light‐hole recombination are observed in the PL spectrum. A large energy difference (about 38 meV) is found between the two peaks, and radiative recombination is dominant in the MQW structure. These are thought to decrease the threshold current of tensile‐strained MQW laser diodes. The MQW active region is thought to be extremely close to the critical conditions for lattice relaxation, but no adverse effects on optical properties are observed. It is concluded that such a tensile‐strained MQW active region has advantages for use as the active region of 630‐nm‐band laser diodes. © 1994 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Self‐consistent finite difference method for simulation and optimization of quantum well electron transfer structures

C. M. Weinert and N. Agrawal

J. Appl. Phys. 76, 7947 (1994); http://dx.doi.org/10.1063/1.357906 (10 pages) | Cited 7 times

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A self‐consistent finite difference method for the simulation of quantum well electron transfer structures is developed and applied to optimize InGaAsP/InP/InAlAs structures for fast optical switching devices. Simultaneous solution of Poisson’s equation, continuity equation, and Schrödinger’s equation on a discretized mesh yields a fast and accurate simulation method which may be applied to arbitrary layer structures and needs no artificial assumptions like abrupt space charge layers. Because of the exact treatment of charge distribution and leakage current the simulation gives new insight into the performance of barrier, reservoir, and quantum well electron transfer structures, which could not be found by previous approximate theories. With this method we calculate the important physical parameters of these devices, namely, the shift of the optical absorption edge, band filling, leakage current, and capacitance. In addition, each layer is investigated separately with respect to its influence on device performance and fabrication tolerances; the results are used for optimization. Moreover, the exact numerical simulation is used to derive simplified relations for the dependence of band filling, capacitance, and high speed behavior on the heterostructure design. © 1994 American Institute of Physics.
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85.30.De Semiconductor-device characterization, design, and modeling
78.66.Fd III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Undoped semi‐insulating GaAs epitaxial layers and their characterization

T. Imaizumi, H. Okazaki, H. Yamamoto, and O. Oda

J. Appl. Phys. 76, 7957 (1994); http://dx.doi.org/10.1063/1.357907 (9 pages) | Cited 4 times

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Wafer annealing was applied to undoped conductive GaAs epitaxial layers grown by the chloride chemical vapor deposition method in order to realize semi‐insulating GaAs epitaxial layers. It was found that, by wafer annealing at temperatures higher than 950 °C, semi‐insulating epitaxial layers with a resistivity higher than 107 Ω cm and a mobility higher than 5000 cm2/V s can be obtained. The material quality has been evaluated by Hall measurement, isothermal capacitance transient spectroscopy, deep level transient spectroscopy, scanning photoluminescence, AB etching, ion implantation, and activation efficiency measurement. It was concluded that the semi‐insulating behavior of undoped GaAs epitaxial layers is due to the increase of the EL2 concentration to the level of 5×1015 cm−3 realized by wafer annealing. The present material does not show any cell structures which are inherent to bulk GaAs materials. It was found to be of the best quality ever reported from the viewpoint of various material characterizations. © 1994 American Institute of Physics.
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73.61.Ey III-V semiconductors
81.40.Rs Electrical and magnetic properties related to treatment conditions
71.55.Eq III-V semiconductors

Physical and electrical investigation of ohmic contacts to AlGaAs/GaAs heterostructures

R. P. Taylor, P. T. Coleridge, M. Davies, Y. Feng, J. P. McCaffrey, and P. A. Marshall

J. Appl. Phys. 76, 7966 (1994); http://dx.doi.org/10.1063/1.357908 (7 pages) | Cited 11 times

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The mechanism by which Ni‐Au‐Ge metallizations establish electrical contact to the two‐dimensional electron gas (2DEG) in modulation‐doped AlGaAs/GaAs heterostructures is investigated. Transmission electron microscopy was used to examine samples after electrical characterization by magnetoresistance measurements at cryogenic temperatures. We present a picture in which a 2DEG of reduced electron density exists under the deposited metallization. The success of the contacting procedure is described in terms of the magnitude of this density and the size, areal density, and penetration depth of a series of metallic spikes which establish the electrical link to the 2DEG. We suggest that the electrical behavior is not dominated by the current injection process at the spike/2DEG interface but is instead dictated by scattering from the array of antidots formed by the spikes and by a dependence of the 2DEG density on the size of the metallic pad. The implications of this picture for future nanostructure devices, featuring patterned ohmic metallization smaller than a micron, are discussed and preliminary results are reported. © 1994 American Institute of Physics.
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73.40.Cg Contact resistance, contact potential
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Schottky diodes with high series resistance: Limitations of forward I‐V methods

V. Aubry and F. Meyer

J. Appl. Phys. 76, 7973 (1994); http://dx.doi.org/10.1063/1.357909 (12 pages) | Cited 38 times

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Some methods have been proposed to deduce the value of Schottky parameters from forward I‐V characteristic even in the presence of a large series resistance. In this paper, some well‐known methods have been applied to experimental data of a real diode and to computer calculated curves. A comparison is made between these methods and the standard procedure. Some indications are given on the validity and the main limitations of all these techniques. © 1994 American Institute of Physics.
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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

Electrical characterization of rapid thermal nitrided and reoxidized plasma‐enhanced chemical‐vapor‐deposited silicon dioxide metal‐oxide‐silicon structures

S. S. Ang, Y. J. Shi, and W. D. Brown

J. Appl. Phys. 76, 7985 (1994); http://dx.doi.org/10.1063/1.357910 (5 pages) | Cited 1 time

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The electrical characteristics of rapid thermal nitrided and reoxidized plasma‐enhanced chemical‐vapor‐deposited (PECVD) silicon dioxide metal‐oxide‐silicon (MOS) structures were investigated. Both nitridation temperature and time affect the properties of the MOS structures as revealed by capacitance‐voltage (C‐V) characteristics. Nitridation at 1000 °C for 60 s followed by reoxidation for 60 s at 1000 °C in an oxygen/nitrogen ambient was found to be superior to the same nitridation followed by reoxidation in pure oxygen. Typical values of fixed charge and interface state densities for devices subjected to nitridation and reoxidation in a mixture of oxygen and nitrogen were 4×1010 cm−2 and 7×1010 eV−1 cm−2, respectively. Avalanche electron injection using electric fields of 3–5 MV/cm produced negative shifts in flatband voltage for low fluence levels and positive flatband voltage shifts for larger fluence levels. Furthermore, the magnitudes of both positive and negative shifts and the electron fluence level at which turnaround occurs increase with electric field. However, independent of the electric field, the flatband voltage saturates very close to its preinjection value. These results strongly suggest that device quality MOS dielectrics can be realized by nitridation/reoxidation of PECVD oxide. © 1994 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Elimination of hydrogen‐related instabilities in Si/SiO2 structures by fluorine implantation

V. V. Afanas’ev, J. M. M. de Nijs, and P. Balk

J. Appl. Phys. 76, 7990 (1994); http://dx.doi.org/10.1063/1.357911 (8 pages) | Cited 6 times

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In this study we have investigated the effect of fluorination on the electrical properties of the Si/SiO2/Al system, including their degradation. Fluorine was introduced by ion implantation into the gate oxide with doses ranging from 109–1015 cm−2. Study of the electron and hole trapping properties of the as‐fabricated system showed that water‐related electron traps and hole traps with small cross section are removed after introduction of fluorine. Hole traps with large cross section related to oxygen vacancies are not affected. Fluorination also suppresses generation of donor‐type interface states and of oxide electron traps generated by vacuum ultraviolet irradiation. The data indicate that the involvement of fluorine is mostly of a catalytic nature. It is proposed that the post‐metallization anneal in the presence of fluorine promotes the elimination of hydrogen available for radiolysis. © 1994 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.61.Ng Insulators
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Hole subband in p‐type channel of semiconductor heterostructures

Kun Liu, J. H. Chu, H. J. Ou, and D. Y. Tang

J. Appl. Phys. 76, 7998 (1994); http://dx.doi.org/10.1063/1.357914 (3 pages) | Cited 2 times

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Based on the characteristics of semiconductor surface capacitance, an experimental model is presented for evaluating the hole subband structures in the p‐type channel of semiconductor heterostructures. For an n‐type InSb metal‐oxide‐semiconductor sample, the capacitance‐voltage spectroscopy is measured and the hole subband structure is derived with using the model presented. The result shows that the Fermi level is always pinned near the bottom of the hole subband, which is attributed to the large density of states of the hole subband. Relevant parameters are also obtained for the hole subband including the subband energy, Fermi level, inversion layer width, and depletion layer width, etc. © 1994 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

New critical‐state model for magnetization of hard type‐II superconductors

T. H. Johansen and H. Bratsberg

J. Appl. Phys. 76, 8001 (1994); http://dx.doi.org/10.1063/1.357917 (4 pages) | Cited 3 times

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We propose a critical‐state model based on the empirical fact that the critical current density Jc in high‐Tc superconductors in some cases is found to decay to an essentially field independent level at large inductions B. The new critical current function, Jc(‖B‖), consists of a constant plus a field dependent term of the Kim model type. Analytical expressions for internal induction profiles and the entire shape of major magnetization loops, as well as the initial branch, are derived for the infinite slab geometry. As an illustration it is shown that the new model gives a precise overall description of a magnetization loop measured for melt processed YBa2Cu3Ox. © 1994 American Institute of Physics.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Ha Magnetic properties including vortex structures and related phenomena

Spatially resolved analysis of high‐Tc grain boundary Josephson junctions and arrays

R. Gerdemann, K.‐D. Husemann, R. Gross, L. Alff, A. Beck, B. Elia, W. Reuter, and M. Siegel

J. Appl. Phys. 76, 8005 (1994); http://dx.doi.org/10.1063/1.357918 (11 pages) | Cited 14 times

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Using Low Temperature Scanning Electron Microscopy (LTSEM) we have studied the spread of the critical current values in one‐ and two‐dimensional arrays of high‐Tc grain boundary Josephson junctions (GBJs). For series arrays the critical current values and the magnetic field dependences of all GBJs within the array could be imaged by LTSEM. Our measurements showed that part of the spread of the critical current values derived from measurements of the current‐voltage characteristics is caused by variations of the local magnetic field at the junction position. For bicrystal GBJs a Gaussian distribution of the critical current values with a spread as small as ±20% was found. For the investigated step‐edge and biepitaxial GBJs the spread of the critical current values was considerably larger. The LTSEM technique also was used to study the spatial homogeneity of the critical current density of the different types of YBa2Cu3O7−δ grain boundary Josephson junctions with a spatial resolution of 1μm. Whereas the critical current density of bicrystal GBJs showed only small variations on this length scale, strong inhomogeneities were found for step‐edge and biepitaxial GBJs. © 1994 American Institute of Physics.
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85.25.Cp Josephson devices
74.50.+r Tunneling phenomena; Josephson effects
74.78.-w Superconducting films and low-dimensional structures

The ac‐Josephson effect above the gap frequency

G. de Lange, J. J. Kuipers, T. M. Klapwijk, R. A. Panhuyzen, H. van de Stadt, and M. W. M. de Graauw

J. Appl. Phys. 76, 8016 (1994); http://dx.doi.org/10.1063/1.357919 (6 pages) | Cited 1 time

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The rf‐power dependence of the ac‐Josephson steps is measured at 720 GHz, using small area Nb tunnel junctions. This frequency is well above the gap frequency of Nb. The junction is placed in a waveguide, and connected to a superconducting stripline, which effectively tunes out the junction capacitance and facilitates the coupling of the radiation to the junction. We observe three Josephson steps, and the first step crosses the zero current axis over a considerable range of rf‐power. This indicates the possible application of THz Josephson steps in voltage standards. The data are compared to the theory and we find clear evidence for the predicted intrinsic roll‐off of the Josephson current amplitude above the gap frequency. © 1994 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
06.20.F- Units and standards
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