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Notes: We report a novel metal–insulator–semiconductor (MIS) structure exhibiting a pseudomorphic In0.05Ga0.95As layer on GaAs with interface state densities in the low 1011 eV−1 cm−2. The structure was grown by a combination of molecular beam epitaxy and chemical vapor deposition methods. The hysteresis and frequency dispersion of the MIS capacitor were lower than 100 mV, some of them as low as 30 mV under a field swing of about ±1.3 MV/cm. The 150-Å-thick In0.05Ga0.95As channel between Si and GaAs is found to bring about a change in the minority carrier recombination behavior of the GaAs channel, in the same way as done by In0.53Ga0.47As channel MIS structures. Self-aligned gate depletion mode In0.05Ga0.95As metal–insulator–semiconductor field-effect transistors having 3 μm gate lengths exhibited field-effect bulk mobility of 1400 cm2/V s and transconductances of about 170 mS/mm. © 1997 American Institute of Physics.

Notes: An analytical solution for minority-carrier current in a heavily doped semiconductor region with a position-dependent band structure has been presented. The solution is general enough to be valid for both degenerate and nondegenerate semiconductors, and for any kind of doping profile. The accuracy of the solution depends on the accuracy of the minority-carrier lifetime model. Such a model developed in the present investigation agrees closely with available experiments.

Notes: A metallization scheme has been developed for obtaining low ohmic contacts to n-GaN with a low contact resistance. The metal contact is a Ti/Al/Ti/Au composite with layers that are respectively 30, 100, 30, and 30 nm thick. Contacts with a specific contact resistivity ρs, as low as 6.0×10−7 Ω cm2 for a doping level of 1.40×1020 cm−3 were obtained after annealing the sample for 30 s at 750 °C in a rapid thermal annealer. The Ti placed on top of the traditional Ti/Al contact appears to have the advantage of tying up the excess Al; therefore it does not form a mottled contact. Some of the additional Ti–Al intermetallic alloys that are formed also have beneficial effects. The Ti–Au layer forms a robust upper portion of the composite, which enables the contacts to have high-temperature applications. © 2001 American Institute of Physics.

Notes: A theoretical method for potential distribution in abrupt heterojunctions (HJs) made of uniformly doped degenerate semiconductors has been developed. The method reduces automatically to that in HJs from nondegenerate semiconductors in the limits of low carrier concentrations. For the development of the method the rigid band approximation of degenerate semiconductors has been considered to be valid. The transport equations of Marshak and Van Vliet [Solid-State Electron. 21, 417 (1978)] and an analytical approximation for the Fermi–Diracintegral of order half by the present author [Solid-State Electron. 30, 713 (1987)] have been employed for the formulation. The average of the scattered experimental data for band-gap narrowing of n-Si, n-Ge, p-GaAs, and n-InP have been fitted to the same form as that for the Fermi–Dirac integral of order 1/2 to ease this formulation. Local electrostatic field and local electrostatic potentials obtained from the formulation reduce to those of Chatterjee and Marshak [Solid-State Electron. 24, 1111 (1981)], Cserveny [Int. J. Electron. 25, 65 (1968)], and Kroemer [J. Appl. Phys. 52, 873 (1981)] under special conditions. It is noted that band-gap narrowing and consideration of Fermi–Dirac statistics represent opposite effects for effective intrinsic carrier concentration and local electrostatic field. At some critical concentration belonging to the degenerate limit of a semiconductor, these two effects cancel the influence of each other on effective intrinsic carrier concentration of the semiconductor and on transition region properties of an HJ. Below this critical concentration, band-gap narrowing rather than a consideration of Fermi–Dirac statistics dominantly influences the device properties. However, above this critical concentration, consideration of Fermi–Dirac statistics dominates over the other. Applications of electrostatic field and electrostatic potential to isotype and anisotype HJs have been discussed. On the basis of present formulas a general form for potential distribution in Schottky barriers has been derived. The relation reduces to that of Gummel and Scarfetter [J. Appl. Phys. 38, 2148 (1967)] under special conditions. Theoretical reasons underlying the lack of rectification in various n-N HJs have been analyzed. In light of this analysis, a theoretical model in terms of many-body electron-electron and electron-donor interactions, and in terms of lowering of band edge in the vicinity of transition region, has been proposed. Numerical results obtained from this model for n-GaAs agree remarkably with observations from experimental measurements.

Notes: A three-dimensional analysis of the validity of emitter-collector reciprocity of double heterostructure bipolar transistors with heavily doped and degenerate base regions has been carried out. The analysis is based on current-density relations of Marshak and Van Vliet [Solid-State Electron. 21, 429 (1978)], an effective intrinsic carrier concentration derived in terms of band-gap narrowing and the effect of Fermi–Dirac statistics, and p-n product derived by considering potential barriers and related properties of heterostructures. The analysis indicates that the bipolar reciprocity holds under low-level injection even when parameters such as band-gap narrowing of the band, and mobility, diffusivity, lifetime, and recombination velocity, etc., of the carriers depend on spatial coordinates, and the carrier concentrations are described by Fermi–Dirac statistics. The analysis is general enough to be applicable to both n-p-n and p-n-p heterostructure and homostructure bipolar transistors.

Notes: An analytical investigation of the space-charge region junction properties of heterojunction semiconductor devices from heavily doped and degenerate semiconductors has been carried out. On the basis of a new formula for Fermi–Dirac integral of order (1)/(2) theoretical formulas for junction boundary conditions, minority-carrier concentrations at the edges of space-charge region and excess minority-carrier concentrations at the edges of space-charge region have been derived. All of these formulas take the spatial dependence of band structures, carrier degeneracy, and band-gap narrowing into account. Under special conditions the formulas reduce to the well-known standard formulas for homojunction devices from both degenerate and nondegenerate semiconductors. The new relation for Fermi–Dirac integral is very highly accurate. Numerical calculations performed on an n-AlzGa1−zAs/p-GaAs (z=0.1) diode indicate that all these parameters significantly influence the junction properties of heterojunction semiconductor devices, and without which theoretical modeling of heterojunction devices with spatially dependent and heavily doped semiconductor regions are likely to involve errors.

Notes: Current-voltage characteristics of AlGaAs/GaAs/AlGaAs double-heterojunction bipolar transistors (DHBTs) grown by molecular beam epitaxy have been studied. DHBTs with both abrupt and graded heterojunctions at the emitter-base and base-collector heterojunctions have been employed for the study. It is noted that DHBTs with abrupt heterojunctions are better than those with graded heterojunctions. These abrupt heterojunctions, along with a nonuniform doping in the base, lead to significantly improved results in current gain and offset voltage. Physical reasons underlying the improvement in the current gain and offset voltage have been analyzed.