Local electronic structures of the native defects in modulation-doped AlAs/GaAs superlattices

Abstract

The authors investigate the character of the native defects (antisites, interstitials, vacancies and complexes of these or with impurities) in undoped and n- or p-type modulation-doped AlAs/GaAs superlattices by means of the developed recursion method. The presented electronic structures, and local and partial density of states give a detailed identification of these defects in various types of AlAs/GaAs superlattice. They have calculated the energies of highly localised electronic states and compared the results with the existing theoretical and experimental data. The stable states of the EL2 defect (AsGa-IAs pair) are studied under the assumption that it has the same atomic configuration as that in the bulk GaAs. With respect to the energy distribution, the electronic occupancy of various defects and of their atomic orbitals are determined; these show the occupied charge states directly. On the basis of these calculations, they find that the ionicity of a normal group III or V atom in AlAs/GaAs superlattices will always be positive when it becomes an interstitial and will be changed with a different type of doping, when it becomes an antisite. By considering the Coulombic nature of a Frenkel pair, some specific complexes between the native defects themselves or with the impurity Si are suggested. Finally, they describe the self-diffusion and the impurity diffusion mechanisms which occur in AlAs/GaAs superlattices with and without doping. Results are compared and contrasted with those of the bulk GaAs materials.

First-Principles Study of Point Defects in GaAs/AlAs Superlattice: the Phase Stability and the Effects on the Band Structure and Carrier Mobility

“…The (GaAs) n /(AlAs) m is one of the most important SL since the development of high electron mobility transistors (HEMT) and quantum cascade lasers (QCLs) a few decades ago [ 1 – 6 ]. Recently with the advances of film epitaxy and nanofabrication techniques, the (GaAs) n /(AlAs) m based SLs and nanodevices with (n + m) ranging from 2 to 10 have demonstrated exciting physical properties related to luminescence and optical absorption, two-phonon absorption, and Raman as well as infrared spectra, which thus found promising applications in optoelectronics, sensing, LED, energy and laser related civilian and industrial areas [ 7 – 12 ]. Meanwhile, toward other critical high-tech applications such as aerospace, high-energy physics, gravitational wave detection, astronomy, space travel, nuclear and national security related areas, the semiconductor SLs and devices are exposed to different radiation environments, i.e., X-ray, neutrons, electrons, ions, etc., which may result in the generation of defects containing impurities, vacancies, interstitials, antisites, and complex of these.…”