Semiconductors are a class of materials that has enabled the development of most modern electronics including tablets, cell phones, and medical diagnostic equipment. Gallium nitride, the semiconductor studied in this project, was the focus of the 2014 Nobel Prize in Physics because its special material properties made possible the energy efficient LED lighting now familiar to many homeowners. Surprisingly, material and structural imperfections are a necessary part of the successful application of this semiconductor. For this reason, the present research project investigates the properties of a certain class of imperfections that act as traps for electrons. Both fundamental and practical information are determined from the electronic and structural studies. In addition to the basic educational benefits afforded students working on this technologically significant issue, students gain first-hand knowledge and learn about potential advances from industrial personnel who actively grow the materials and devices.
is designed to better understand the acceptor impurities in GaN by microscopically investigating their structure and charge state. The specific focus is electron paramagnetic resonance (EPR) measurements of mm-thick free-standing crystals of GaN doped with technologically important acceptors such as magnesium and carbon. Until recently, EPR of GaN has been hampered by the limited total number of defects and non-uniform strain inherent to thin films. The availability of thick free-standing GaN crystals increases the number of detectable centers and minimizes strain, thus enabling the study of characteristics uniquely addressed by EPR, such as charge state and local structure. In addition, the potential influence of the defects on device properties is investigated with the help of a GOALI partner, Kyma Tech. The study provides previously unavailable fundamental properties such as defect symmetry, and the determination of practical information such as association of a specific defect with an energy level. Overall, the results enhance the understanding of the role of point defects in both bulk and thin film acceptor-doped GaN.
