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TITLE:
A Short but Bright Life - Coherent Spontaneous Emission of
Excitons in ZnO
SPEAKER:
Gang Xiong,
TIME: Thursday Nov. 4, 2004
at 3 PM*
PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)
Wake Forest University
*Note special time.
Certain properties of ZnO, including remarkably fast sub-nanosecond lifetime of excitonic recombination luminescence, have suggested to us and others that coherence properties are important to the observations. Following experimental measurements and analysis in term of giant oscillator strength by my colleague John Wilkinson, I undertook as one goal of this dissertation research to understand the coherent spontaneous radiation by excitons, especially the theory of giant oscillator strength. I present a formal derivation of this theory in which a single exciton emits radiation as a coherent array. We examine the dependence of transition rate on the size of the coherent source volume, and investigate how phase cancellation will affect the overall transition rate. Results suggest the transition rate is tunable via adjusting particle size or coherence volume, taking into account phase cancellation at off-axis directions. This topic leads naturally to exciton polaritons, and we have conducted a time-of-light study of bound-exciton polariton dispersive propagation in ZnO. Recently ZnO has attracted a lot of interest for its potential application as a uv laser diode. Although great progress has been made to realize this goal, challenges remain in particular at exploring reliable recipes for fabricating high quality p-type ZnO. In this dissertation we discuss our preliminary effort on fabricating p-type ZnO samples. ZnO thin films have been produced via sputtering and pulsed laser deposition techniques. The structure, optical and electric characterizations were conducted on our home-grown thin films samples. In addition, donor-acceptor pair luminescence has been observed from nitrogen-implanted single crystal ZnO.