Computational studies of III-V compound semiconductors

Abstract

Nitrogen-containing III-V compound semiconductors are uniquely suited for many applications in electronics and optoelectronics. For example, the wide-band-gap semiconductor GaN and its alloys are essential for many recently developed optoelectronic devices such as white light emitting diodes (LEDs) and lasers with colors from red to ultraviolet. The electrical and optical properties of semiconductor materials are mainly determined by a small number of defects and impurities that have been intentionally or unintentionally incorporated into the material. In a compound semiconductor the compositional uniformity can also have an important effect on the electronic properties of the alloy. In this thesis these issues are studied in III-V compound semiconductors with computational modeling. A density-functional theory (DFT) based method is used to determine the structure and energetics of 1) vacancies and substitutional As and In defects in GaN, 2) N interstitial defects in GaAs, 3) vacancies in AlN and 4) GaAsN and GaInN alloys. The results from the defect calculations for the various systems include the most prevalent types of the defects and their most important properties under different growth conditions. Compositional instability in GaInN is studied with multiscale modeling where interaction parameters for the lattice kinetic Monte Carlo simulations of the alloy decomposition are taken from the DFT calculations. The simulations show the high sensitivity of the GaInN decomposition to relatively small variations of the interaction between Ga and In atoms and offer an explanation for the diversity of the alloy decomposition patterns observed in the experiments.