Cyrus Dreyer Seminar
12:30 pm - 1:30 pm, plus 30 minutes of Q & A
SERC Building, room 703
Title: Sources of Shockley-Read-Hall recombination in III-Nitrides
Speaker: Cyrus Dreyer, Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey
For individuals who will not be on Temple's campus, Dr. Dreyer's lecture can be accessed through Webex. The meeting number is 646 025 516.
Shockley-Read-Hall (SRH) recombination at defects is an important loss mechanism in a variety of semiconductor devices, including light emitting diodes (LEDs) and solar cells. In order to improve the efficiency of such devices, it is desirable to predict theoretically which defects and/or impurities will act as SRH recombination centers, and what the recombination rate will be. This requires knowledge of the defects/impurities that may be present, the position of the defect/impurity levels in the band gap of the semiconductor, and the mechanisms and rates at which electrons and holes are captured at the defect levels. We have applied a recently developed, first-principles methodology for determining capture rates to the case of SRH in the group III-nitrides (specifically GaN and InGaN alloys), key materials for solid-state general lighting and display technology. Loses due to SRH have been experimentally measured in InGaN-based LEDs, however the microscopic mechanisms and specific defects responsible are unknown. We find that for the InGaN alloys used for devices emitting at green and yellow wavelengths, gallium vacancies complexed with hydrogen and/or oxygen will act as SRH centers with rates detrimental to device performance. For wider band gap InGaN alloys (blue and violet wavelengths), we show that a novel mechanism involving the excited electronic states of the defects is required to explain the experimentally observed SRH recombination; we demonstrate this mechanism using the example of a specific Ga vacancy complex. Finally, I will comment on other potential SRH centers in these materials.
Cyrus Dreyer is a postdoctoral associate in the Theoretical Condensed Matter group in the department of Physics and Astronomy at Rutgers University, working with David Vanderbilt and Karin Rabe. His research involves developing and implementing first-principles methods based on density functional theory to explore materials for electronic and optoelectronic devices. His interests include group III-nitrides, novel ferroelectric materials, complex oxides and their heterostructures, applications of the modern theory of polarization, point defects in semiconductors, and flexoelectricity.