The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

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A comprehensive review of zno materials and devices

We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

Band parameters for III–V compound semiconductors and their alloys

A review is given of our present knowledge of metal-semiconductor contacts. Topics covered include the factors that determine the height of the Schottky barrier, its current/voltage characteristics, and its capacitance. A short discussion is also given of practical contacts and their application in semiconductor technology, and a comparison is made with p-n junctions.

Metal-semiconductor contacts

The Al x Ga1−x As/GaAs heterostructure system is potentially useful material for high‐speed digital, high‐frequency microwave, and electro‐optic device applications Even though the basic Al x Ga1−x As/GaAs heterostructure concepts are understood at this time, some practical device parameters in this system have been hampered by a lack of definite knowledge of many material parameters Recently, Blakemore has presented numerical and graphical information about many of the physical and electronic properties of GaAs [J S Blakemore, J Appl Phys 5 3, R123 (1982)] The purpose of this review is (i) to obtain and clarify all the various material parameters of Al x Ga1−x As alloy from a systematic point of view, and (ii) to present key properties of the material parameters for a variety of research works and device applications A complete set of material parameters are considered in this review for GaAs, AlAs, and Al x Ga1−x As alloys The model used is based on an interpolation scheme and, therefore, necessitates known values of the parameters for the related binaries (GaAs and AlAs) The material parameters and properties considered in the present review can be classified into sixteen groups: (1) lattice constant and crystal density, (2) melting point, (3) thermal expansion coefficient, (4) lattice dynamic properties, (5) lattice thermal properties, (6) electronic‐band structure, (7) external perturbation effects on the band‐gap energy, (8) effective mass, (9) deformation potential, (10) static and high‐frequency dielectric constants, (11) magnetic susceptibility, (12) piezoelectric constant, (13) Frohlich coupling parameter, (14) electron transport properties, (15) optical properties, and (16) photoelastic properties Of particular interest is the deviation of material parameters from linearity with respect to the AlAs mole fraction x Some material parameters, such as lattice constant, crystal density, thermal expansion coefficient, dielectric constant, and elastic constant, obey Vegard’s rule well Other parameters, eg, electronic‐band energy, lattice vibration (phonon) energy, Debye temperature, and impurity ionization energy, exhibit quadratic dependence upon the AlAs mole fraction However, some kinds of the material parameters, eg, lattice thermal conductivity, exhibit very strong nonlinearity with respect to x, which arises from the effects of alloy disorder It is found that the present model provides generally acceptable parameters in good agreement with the existing experimental data A detailed discussion is also given of the acceptability of such interpolated parameters from an aspect of solid‐state physics Key properties of the material parameters for use in research work and a variety of Al x Ga1−x As/GaAs device applications are also discussed in detail

GaAs, AlAs, and AlxGa1−xAs: Material parameters for use in research and device applications

Theoretical models of Schottky-barrier height formation are reviewed. A particular emphasis is placed on the examination of how these models agree with general physical principles. New concepts on the relationship between interface dipole and chemical bond formation are analyzed, and shown to offer a coherent explanation of a wide range of experimental data.

Recent advances in Schottky barrier concepts

Heterojunctions and Metal Semiconductor Junctions

The physical properties of GaSb are briefly presented and the device implications reviewed. GaSb is a direct gap semiconductor (0.72 eV) capable of being doped either p or n type with good mobilities and it has significant electro-optical potential in the near IR range. As a substrate, or active layer, GaSb can be employed in conjunction with many semiconductors such as (AlGa)Sb or In(AsSb) and has interesting heterojunction potential for detectors and lasers and quantum well structures.

Gallium antimonide device related properties

Indium arsenide is a direct gap semiconductor (036 eV at 300 K and 040 eV at 77 K) with high electron mobility (greater than 20 000 cm2V-t-1s−1 at 300 K and approximately 60 000 cm2V−1s−1 at 77 K) The hole mobilities are in the range 100–400 cm2V−1s−1 Its electro-optical properties are of interest for the IR range out to about 3 μm and to 8 μm in conjunction with In(As,Sb) alloys Lattice matched heterojunctions can be obtained with alloys such as AlxGa1−x- AsySb1−y InAs has also been grown on a range of non-lattice-matched semiconductors such as GaSb, InP, GaAs and AlSb, and has exhibited interesting quantum well actions The field effect transistor (FET) and modulated doped field effect transistor (MODFET) properties are promising but have not been fully developed The low field for avalanche action (about 105V−1s−1 presents some device limitations

Indium arsenide: a semiconductor for high speed and electro-optical devices

Horizontal Bridgman grown n‐type GaAs is shown to contain two important electron traps EL6 (035 eV) and EL2 (080 eV) in the 1015 cm−3 concentration range A heat treatment at 800 °C for 1 h results in the reduction of EL6 to about 1013 cm−3 to a depth of at least 10 μm and an increase in EL2 by an amount about equal to the reduction of EL6 Measurement of the minority‐carrier (hole) diffusion lengths in this depth range by an electron beam induced current (EBIC) technique shows an inverse correlation with the concentration of the EL6 trap The results may be explained if EL6 is assumed to be VGa‐VAs, EL2 to be AsGa‐VAs, and the interaction between the two traps to involve Asi

Evidence for EL6 (Ec− 0.35 eV) acting as a dominant recombination center in n‐type horizontal Bridgman GaAs

Semiconductor heterojunctions with ideal lattice matching, well-controlled in fabrication, yield devices that cannot be achieved in any other way. These devices include modulated-doped high-speed field-effect transistors, ultra-high-gain and high-speed bipolar transistors, efficient injection lasers and light-emitting diodes and sensitive photo-detecting structures. Atomic reconstructions take place at heterojunction interfaces and are process-fabrication-dependent and not adequately understood. The barrier discontinuities observed are therefore scattered in value and also somewhat dependent on the determination method. Many papers in this Special Issue contain review aspects of these matters. Others, however, are specific contributions on very particular heterojunction topics. Not all aspects of heterojunctions are dealt with by the papers that follow, and the present article is intended for newcomers to the field as a brief commentary on topics that are not adequately represented.

A. G. Milnes

Papers

Heterojunctions and Metal Semiconductor Junctions

Gallium antimonide device related properties

Indium arsenide: a semiconductor for high speed and electro-optical devices

Evidence for EL6 (Ec− 0.35 eV) acting as a dominant recombination center in n‐type horizontal Bridgman GaAs

Semiconductor heterojunction topics: Introduction and overview