A. Sher

Theory of AlN, GaN, InN and their alloys

Abstract This review focuses on the fundamental properties of III–V compound semiconductors from a theoretical or computational standpoint. Its purpose is to summarize the contributions of electronic structure theory to the present context and to provide some foundations for the modern techniques. This will enable one to assess the limitations of the techniques employed previously.

InTlP — a proposed infrared detector material

In1−xTlxP is proposed as a promising material for infrared detectors. A number of key optical and structural properties are studied within local density‐functional theory. In1−xTlxP at x=0.67 and In1−xTlxAs at x=0.15 are estimated to have a gap of 0.1 eV. Their binding energies are larger than that of InSb, and they are found to form stable zinc‐blende alloys for all x. In1−xTlxP nearly lattice matches to InP, and offers the potential to integrate detector array and read‐out circuit.

Generalized Brooks’ formula and the electron mobility in SixGe1−x alloys

A formula for alloy‐scattering‐limited electron mobility in semiconductors is obtained for indirect gap systems with multiple band minima. All the input parameters needed are defined explicitly. The drift mobility of SixGe1−x which has a dip at x ∼0.13 and a broader minimum at x ∼0.5 is calculated by adding alloy scattering to other scattering mechanisms and correlates well with the measured Hall mobility.

InTlSb: An infrared detector material?

In1−xTlxSb is proposed as promising infrared material. A number of optical and structural properties are studied within local density‐functional theory. The alloy at x=0.09 is estimated to have a gap of 0.1 eV. Although TlSb is found to favor the CsCl structure, the zinc blende alloy is stable for low x values. A phase diagram is calculated to estimate the regions of stable phases and explore the conditions for growing narrow‐gap In1−xTlxSb alloys.

Band gap variation and lattice, surface, and interface ‘‘instabilities’’ in Hg1−xCdxTe and related compounds

This paper brings into focus the differences between Hg1−xCdxTe (MCT) and ‘‘ordinary’’ semiconductors such as column 4, 3–5, and most 2–6 compounds. The key characteristic of MCT which makes it both different and of practical interest is the variation of band gap with composition (0 to 1.5 eV). This paper shows that this benefit is not without its difficulties. In particular, the same unusual characteristic of the Hg atomic states which leads to the advantageous movement of  band gap with composition weakens the bonding of Hg in the lattice. This bonding weakness exhibits itself in many ways in the characteristics of MCT, both at surfaces and interfaces and in the bulk. Because of this there is a potential instability associated with the surface or interface; however, this instability depends critically on the crystalline perfection of the MCT to depths far below the surface. The reason for this is defects move from the bulk to the surface (or in the opposite direction) with surprising ease—even at room t...

Structural properties of bismuth-bearing semiconductor alloys

Materials currently used for detection in the infrared spectral region have notoriously poor structural properties. In search of a better narrow‐gap material, we have addressed the structural properties of bismuth‐bearing III‐V semiconductor alloys theoretically. Because the Bi compounds are not known to form zinc‐blende structures, only the anion‐substituted alloys InPBi, InAsBi, and InSbBi are considered candidates as narrow‐gap semiconductors. We calculate the bond energies and lengths for the zinc‐blende Bi compounds and their diluted and concentrated alloys. Strain coefficients for the compounds are calculated, and predictions for the mixing enthalpies, miscibility gaps, and critical temperatures are made. Miscibility calculations indicate that InSbBi will be the most miscible, and because of the large lattice mismatch of the constituents, InPBi will be the most difficult to mix. Tendencies toward cluster formation and deviations from randomness in the alloys are considered. Calculations of the hardn...

AMPHOTERIC BEHAVIOR OF ARSENIC IN HGCDTE

The properties of arsenic in HgCdTe are predicted using ab initio calculations and a statistical theory. Predictions on the amphoteric nature of arsenic are in good agreement with experimental results on material growth both by liquid phase epitaxy and molecular beam epitaxy (MBE). The experimentally observed dependence of the arsenic diffusion on mercury partial pressure is also explained by our results. A microscopic model for activating the arsenic as an acceptor is suggested, and requirements of post-MBE-growth activation anneals are identified.

Bandstructure effect on high-field transport in GaN and GaAlN

The velocity-field characteristics in zinc-blende GaN are calculated from the Boltzmann equation, using realistic energy bands taken from ab initio theory. The drift velocity and the high-field negative differential resistance are shown to be largely determined by the inflection point in the bands centered around the Γ valley, instead of the usual intervalley scattering. We analyze the relative importance of these competing mechanisms for GaN and Al0.5Ga0.5N. The importance of this anomaly to device properties is also discussed.

Electrical properties of epitaxially grown CdTe passivation for long‐wavelength HgCdTe photodiodes

Results of experimental measurements and theoretical analysis are presented for the TiAu/ZnS/CdTe/HgCdTe metal–insulator–semiconductor heterostructure. The passivation of HgCdTe is provided by a double layer consisting of a dielectric ZnS placed on top of an epitaxial CdTe layer. Both HgCdTe and CdTe were grown by metalorganic chemical vapor deposition. Two types of CdTe layers were investigated: one was grown directly, in situ, immediately following the growth of HgCdTe; the second was grown indirectly using previously grown HgCdTe samples. It is shown that directly grown CdTe layers lead to low fixed interface charge, which is a good condition for passivation. The indirectly grown samples are still acceptable, but not as good as the directly grown samples. We demonstrate, on the basis of theoretical considerations, that the dielectric ZnS improves the flatband condition at the CdTe/HgCdTe interface.

Defects in ZnTe, CdTe, and HgTe: Total energy calculations

Total energies for various impurities and defects in HgTe, CdTe, and ZnTe are calculated. Calculations were done using a self‐consistent linear muffin‐tin orbital (LMTO) method within the local density and atomic spheres approximation. We calculate the total energy for substitution on both lattice and interstitial sites, and estimate the lattice strain energies. Estimates of the variation with the alloy predict a linear variation of the substitution energy with the local concentration. We predict that the Te antisite will be more prevalent in all three of the compounds than previously thought. The problem of cross doping during heteroepitaxy on GaAs is predicted to be greater on the cation sublattice.