FIRST-PRINCIPLES AND ATOMISTIC MODELING OF POLARIZATION AND AUGER PROCESSES IN WURTZITE NANOWIRE OPTICAL DEVICES

Author

Ye Wu, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2019

Degree Name

Doctor of Philosophy

Department

Electrical and Computer Engineering

First Advisor

Ahmed, Shaikh

Abstract

Optoelectronics devices constitute a branch of the semiconductor family with a broad application domain; however, device efficiency and reliability have always been a significant concern. This work uses first-principles modeling to study the fundamental causes and, combined with multiscale computational simulations, investigate factors influencing device reliability. Specifically, our goal is to understand the fundamental physics concerning two essential degradation mechanisms in novel optoelectronic materials, namely, the piezoelectric polarization and the Auger recombination, both adversely affecting the device conversion efficiency.First, we evaluate and compare the piezoelectric properties in bare ZnO and ZnO/MgO core-shell nanowires. The study confirms that the effective piezoelectric coefficient in bare ZnO nanowires is a highly diameter sensitive parameter. In the thinnest ZnO nanowire, with only one layer of atoms, the effective piezoelectric coefficient attains a maximum value of 12.21 C/m2. On the other hand, for the first time, we report that piezoelectricity in MgO-passivated ZnO nanowires exhibits a lesser size dependence than in the bare ones, a finding that may prove useful in the design of emerging ultraviolet optoelectronic devices.Next, we study the effects of Auger recombination in recently reported InGaN/GaN dot-in-wire light emitters. In wurtzite III-Nitride nano-devices, the non-radiative Auger recombination is the primary mechanism responsible for the degradation of internal quantum efficiency (IQE), especially under high current density. The Auger recombination coefficient is calculated using the atomistic simulator NEMO 3-D combined with a 3-D Poisson solver. Effects of strain and polarization, which can be strong in realistically-sized structures, have been taken into account while modeling these structures. We demonstrate that the use of soft-confinement at the quantum dot interface or larger nanowire leads to a suppression of Auger recombination compared to the sharp-interface or thinner nanowire counterparts. The atomistically simulated Auger recombination coefficient for the quantum well core with different diameter is then incorporated into a TCAD simulator to obtain the device terminal characteristics. The simulation results indicate that increasing the dot volume remains the most efficient way to improve the IQE of the InGaN/GaN dot in wire light emitters.