UC Santa Barbara

The nonradiative recombination of electrons and holes in semiconductors is inherently detrimental to the performance of optoelectronic technologies. Two types of recombination mechanism cause the loss of carriers at different carrier density regimes: Shockley-Read-Hall recombination dominates at low carrier-densities and Auger recombination dominates at high carrier densities. Shockley-Read-Hall recombination can be considered as the independent capture of electrons and holes by a crystal defect or impurity via interactions with lattice vibrations. Auger recombination is a three-carrier process that involves an electron and a hole recombining across the band gap with the excess energy of that recombination going to a third carrier (either an electron or a hole). In this thesis, we discuss the simulation of these two distinct types of nonradiative recombination mechanisms using first-principles calculations by presenting case studies of the nonradiative recombination in several different material systems.

Recently, unexpectedly large concentrations of calcium have been found in InGaN quantum wells, likely due to unintentional contamination during the polishing process or from the In source. We assess the role of Ca impurities in pure GaN and InGaN alloys and identify it as a deep donor. Using our methodology for simulating the Shockley-Read-Hall recombination we will demonstrate that the Ca impurity readily assists in nonradiative recombination and is a detrimental recombination center in lower band gap InGaN alloys.

For Auger recombination, we look at two material systems (InAs and CH3NH3PbI3) where the spin-orbit interactions play a large role in the electronic structure. Both InAs and CH3NH3PbI3 exhibit a resonance between the band gap and the spin-orbit splitting, and we examine how this splitting affects the Auger recombination in each case. In the case of InAs, we also examine the impact of the indirect, phonon-assisted, Auger process on the recombination rate. For CH3NH3PbI3, the Rashba-type linear-k splitting at the band edges has been flagged as a key feature in the band structure. We demonstrate how this splitting influences the Auger process, and propose how Auger recombination can be suppressed in this material.