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

Thermoelectric materials are of interest for applications as heat pumps and power generators. The performance of thermoelectric devices is quantified by a figure of merit, ZT, where Z is a measure of a material's thermoelectric properties and T is the absolute temperature. A material with a figure of merit of around unity was first reported over four decades ago, but since then-despite investigation of various approaches-there has been only modest progress in finding materials with enhanced ZT values at room temperature. Here we report thin-film thermoelectric materials that demonstrate a significant enhancement in ZT at 300 K, compared to state-of-the-art bulk Bi2Te3 alloys. This amounts to a maximum observed factor of approximately 2.4 for our p-type Bi2Te3/Sb2Te3 superlattice devices. The enhancement is achieved by controlling the transport of phonons and electrons in the superlattices. Preliminary devices exhibit significant cooling (32 K at around room temperature) and the potential to pump a heat flux of up to 700 W cm-2; the localized cooling and heating occurs some 23,000 times faster than in bulk devices. We anticipate that the combination of performance, power density and speed achieved in these materials will lead to diverse technological applications: for example, in thermochemistry-on-a-chip, DNA microarrays, fibre-optic switches and microelectrothermal systems.

Thin-film thermoelectric devices with high room-temperature figures of merit

We present a comprehensive and up-to-date compilation of band parameters for all of the nitrogen-containing III–V semiconductors that have been investigated to date. The two main classes are: (1) “conventional” nitrides (wurtzite and zinc-blende GaN, InN, and AlN, along with their alloys) and (2) “dilute” nitrides (zinc-blende ternaries and quaternaries in which a relatively small fraction of N is added to a host III–V material, e.g., GaAsN and GaInAsN). As in our more general review of III–V semiconductor band parameters [I. Vurgaftman et al., J. Appl. Phys. 89, 5815 (2001)], complete and consistent parameter sets are recommended on the basis of a thorough and critical review of the existing literature. We tabulate the direct and indirect energy gaps, spin-orbit and crystal-field splittings, alloy bowing parameters, electron and hole effective masses, deformation potentials, elastic constants, piezoelectric and spontaneous polarization coefficients, as well as heterostructure band offsets. Temperature an...

Band parameters for nitrogen-containing semiconductors

Status and future outlook of III-V compound semiconductor visible-spectrum light-emitting diodes (LEDs) are presented. Light extraction techniques are reviewed and extraction efficiencies are quantified in the 60%+ (AlGaInP) and ~80% (InGaN) regimes for state-of-the-art devices. The phosphor-based white LED concept is reviewed and recent performance discussed, showing that high-power white LEDs now approach the 100-lm/W regime. Devices employing multiple phosphors for "warm" white color temperatures (~3000-4000 K) and high color rendering (CRI>80), which provide properties critical for many illumination applications, are discussed. Recent developments in chip design, packaging, and high current performance lead to very high luminance devices (~50 Mcd/m2 white at 1 A forward current in 1times1 mm2 chip) that are suitable for application to automotive forward lighting. A prognosis for future LED performance levels is considered given further improvements in internal quantum efficiency, which to date lag achievements in light extraction efficiency for InGaN LEDs

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Status and Future of High-Power Light-Emitting Diodes for Solid-State Lighting

The III-nitrides include the semiconductors AlN, GaN and InN, which have band gaps spanning the entire UV and visible ranges. Thin films of III-nitrides are used to make UV, violet, blue and green light-emitting diodes and lasers, as well as solar cells, high-electron mobility transistors (HEMTs) and other devices. However, the film growth process gives rise to unusually high strain and high defect densities, which can affect the device performance. X-ray diffraction is a popular, non-destructive technique used to characterize films and device structures, allowing improvements in device efficiencies to be made. It provides information on crystalline lattice parameters (from which strain and composition are determined), misorientation (from which defect types and densities may be deduced), crystallite size and microstrain, wafer bowing, residual stress, alloy ordering, phase separation (if present) along with film thicknesses and superlattice (quantum well) thicknesses, compositions and non-uniformities. These topics are reviewed, along with the basic principles of x-ray diffraction of thin films and areas of special current interest, such as analysis of non-polar, semipolar and cubic III-nitrides. A summary of useful values needed in calculations, including elastic constants and lattice parameters, is also given. Such topics are also likely to be relevant to other highly lattice-mismatched wurtzite-structure materials such as heteroepitaxial ZnO and ZnSe.

https://iopscience.iop.org/article/10.1088/0034-4885/72/3/036502/pdf

X-ray diffraction of III-nitrides

We report on phase separation in thick InGaN films with up to 50% InN grown by metalorganic chemical vapor deposition from 690 to 780 °C. InGaN films with thicknesses of 0.5 μm were analyzed by θ–2θ x-ray diffraction, transmission electron microscopy (TEM), and selected area diffraction (SAD). Single phase InGaN was obtained for the as-grown films with <28% InN. However, for films with higher than 28% InN, the samples showed a spinodally decomposed microstructure as confirmed by TEM and extra spots in SAD patterns that corresponded to multiphase InGaN.

Phase separation in InGaN grown by metalorganic chemical vapor deposition

Violet/blue photoluminescence was observed from epitaxial cerium oxide films on silicon substrates. The films were deposited on silicon (111) substrates under ultrahigh vacuum conditions using pulsed laser ablation of a cerium oxide target and treated by rapid thermal annealing in argon. High resolution transmission electron microscopy and x-ray diffraction measurements indicated the formation of a single crystal cerium oxide phase Ce6O11 different from CeO2 in the annealed films. The emission might be due to charge transfer transitions from the 4f band to the valence band of the oxide.

Violet/blue emission from epitaxial cerium oxide films on silicon substrates

We describe a simple, yet phenomenologically very different, low-temperature modification to the conventional metal–organic chemical vapor deposition. It has been applied to the epitaxy of hexagonal-phased Bi2Te3/Sb2Te3 superlattices on zinc-blende GaAs substrates. The modification enables a two-dimensional, layer-by-layer, epitaxy instead of a three-dimensional islanded growth. Therefore, this approach is of generic importance to the epitaxy of many electronic and magnetic materials and their superlattices. High-resolution transmission electron microscopy studies indicate that the interface between the GaAs substrate and Bi2Te3 film is qualitatively defect free and that periodic structures are formed in the Bi2Te3/Sb2Te3 superlattices, with one of the individual layers as small as 10 A. Such ultra-short-period superlattices offer significantly higher carrier mobilities than their respective solid-solution alloys, apparently due to the elimination of alloy scattering and the minimal effects of random inte...

Low-temperature organometallic epitaxy and its application to superlattice structures in thermoelectrics

We present an approach to determine the critical layer thickness in the InxGa1−xN/GaN heterostructure based on the observed change in the photoluminescence emission as the InxGa1−xN film thickness increases. From the photoluminescence data, we identify the critical layer thickness as the thickness where a transition occurs from the strained to unstrained condition, which is accompanied by the appearance of deep level emission and a drop in band edge photoluminescence intensity. The optical data that indicate the onset of critical layer thickness, was also confirmed by the changes in InxGa1−xN surface morphology with thickness, and is consistent with x-ray diffraction measurements.

Determination of the critical layer thickness in the InGaN/GaN heterostructures

Band gap measurements have been carried out in strained and relaxed InxGa1−xN epilayers with x<0.25. Values of x were determined from x-ray diffraction of relaxed films. The lowest energy absorption threshold, measured by transmittance, was found to occur at the same energy as the peak of the photoluminescence spectrum. Bowing parameters for both strained and relaxed films were determined to be 3.42 and 4.11 eV, respectively. The dependence of the band gap shift, ΔEg, on strain is presented.

S. X. Liu

Papers

Phase separation in InGaN grown by metalorganic chemical vapor deposition

Violet/blue emission from epitaxial cerium oxide films on silicon substrates

Low-temperature organometallic epitaxy and its application to superlattice structures in thermoelectrics

Determination of the critical layer thickness in the InGaN/GaN heterostructures

Optical band gap dependence on composition and thickness of InxGa1−xN (0<x<0.25) grown on GaN