Band Structure And Device Design Study Of Inas/(In)GaSb Superlattice

The electronic band structures, mechanical and optical properties of InAs/(In)GaSb superlattice systems are systematically studied by k·p theory and first-principles calculations. The essential issues concerning InAs/(In)GaSb superlattice systems in optoelectronic applications are intensively investigated: structure optimization, Auger lifetime, interface structure and relaxation, low-dimensional systems (atomic chain, nanowire and nanotube superlattices). Based on these calculations, a novel two-color infrared photodetector is designed to fulfill dual-waveband photon detection at a single detection material (active region of device). At the end of the dissertation, an infrared laser generation mechanism without population inversion between subbands in low-dimensional semiconductor heterostructures such as InAs/(In)GaSb superlattices are theoretically analyzed and discussed.The research background, material properties and physics of InAs/(In)GaSb superlattices, some primary optoelectronic devices and general methods of band structure calculations are introduced. Density functional theory and corresponding numerical methods have been greatly developed in recent years and now are extensively applied in the research fields of physics, chemistry, materials and biology. The fundamental theory of first-principles (Density functional theory) and its expansions developed in recent years are reviewed, and some widely used computational packages for first-principles calculation are introduced.The band structures and optical properties of free-standing [001] InAs/InxGa1-xSb superlattices applied in long wavelength infrared detection are systematically calculated by 8 bands k·p theory in envelope function approximation, including: energy levels and dispersions of subbands, cutoff wavelengths, widths of C1 and HH1 minibands, momentum matrix elements, C1 zone-center effective masses. The calculation results are discussed and analyzed in term of structure optimization, indicating optimized structures in specified regions of structure parameters. We demonstrate theoretically that optimized InAs/InxGa1-xSb superlattices are promising candidates for high efficient photodetector in long wavelength infrared range (LWIR, 8?14μm).InAs/InxGa1-xSb superlattice structures are optimized for high detectivity LWIR detectors by adjusting structure parameters in terms of simultaneous inhibitions of three Auger processes, using the eight-band k·p theory for energy band structure calculations. We present theoretically the technologically essential Auger recombination lifetimes in narrow-gap semiconductor superlattices by a fully first-principles formalism, based on accurate energy bands and wave functions provided by the full-potential linearized augmented plane wave scheme. Auger lifetimes determined by the two methods exhibit good agreement for n-doped HgTe/CdTe and InAs/InxGa1-xSb superlattices with experimentally measured values. This demonstrates the computational formalism as a new sensitive tool in Auger lifetime prediction for the synthetic narrow-gap semiconductor superlattices.First-principles all electron relativistic calculations within general gradient approximation are implemented to investigate the interface structure, electronic and optical absorption properties of quaternary InAs/GaSb superlattices with InSb or GaAs type of interface, emphasizing on the consideration and analysis of atomic relaxations at superlattice interfaces. The electronic total energies of InAs/GaSb superlattices are calculated to determine the relaxed interface structures. The calculated results indicate that the chemical bonding and ionicity of anion atoms are essentially important in determining the interface and band structures of InAs/GaSb superlattices.Three low-dimensional structures of InAs/GaSb superlattices are studied by first-principles calculations, including three parts. In the first part, the atomic structures, mechanical properties, electronic and phonon structures, quantum transport and optical properties of InAs/GaSb atomic chain superlattices are calculated by first-principles pseudopotential plane wave scheme and the method combining DFT numerical basis set expansion and nonequilibrium Green’s function. Compared with InAs/GaSb superlattices with layer structures, the band structures of InAs/GaSb atomic chain superlattices are explicitly different, and vary with double-atoms number in supercell, exhibiting metallic characteristic for some cases. The stabilities of InAs/GaSb atomic chain superlattices are investigated by analysis of phonons in full Brillouin zone. The calculated results of quantum transport indicate that the conductances vary with chain length and strain. Optical absorption results of some structures exhibit precipitous absorption edges, with the cutoff wavelength changing with the different structures. In the second part, the structural, electronic, mechanical and optical properties of (InAs)1/(GaSb)1 nanowire superlattices (subscripts denote molecular or double-atoms number) with the axis along [001] and [111] zincblende crystallographic orientations are calculated by first-principles schemes similar to the first part. The results indicate that radial lattice constants decrease with the reduced wire diameters due to surface effects. Young’s modulus and Poisson’s ratio decreases and increases with the reduced wire diameters, similar to nanowires constituted from single material. The band-gaps vary with wire diameters as 1/Dn (D denotes wire diameter, n<1). The variations of band energy dispersions with axial strain result in the changes of effective masses, and even induce transformations from direct to indirect band-gaps in small wire diameter structures. In the third part, the structural and electronic properties of (10, 0) InAs, GaSb, InxGa1-xSb nanotubes and InAs/InxGa1-xSb nanotube superlattices are calculated by first-principles pseudopotential plane wave scheme. InAs, GaSb and InxGa1-xSb nanotubes exhibit semiconductor direct band-gaps. InAs/InxGa1-xSb nanotube superlattices (0<x<0.4) exhibit the type-II broken-gap band-edge alignments, and the superlattice band-gap significantly varies with the structures of nanotube superlattices.At the end, we design a novel structure InAs/InxGa1-xSb superlattice two-color photodetector to fulfill simultaneously the short and long wavelength infrared detections in the same operation area of a detective material, in which special doping and layer structure and double external electrocircuits have been utilized to separate and detect photocurrents of the two infrared spectra. The simulated photon responsivities of the two infrared spectra are comparable to some reported values for the corresponding single-color photodetector. We also present an infrared generation mechanism without population inversion between subbands in quantum well, superlattice and quantum dot lasers. The infrared generation scheme is based on the resonant nonlinear mixing of the two optical laser fields which are from two interband transitions in the same active region and serve as the coherent drive for infrared field. In ideal conditions, the intrinsic down-conversion efficiency can reach the limiting quantum value. Because the proposed infrared generation is parametric, the proposed scheme without population inversion is especially promising for LWIR operation.