Temperature Dependence of Bound Exciton Emissions in GaN
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ysics Department, Emory University, Atlanta, GA 30322 Institute of Material Research and Engineering, Singapore, 119260 c) Physics Department and Microelectronics Research Center, Iowa State University, Ames, IA 50011 d) School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA 30332 e) Emcore Corporation, Somerset, NJ 08873 † Work initiated when ZCF was with Emcore Corp. ‡ Work initiated when SER was with Emory University b)
Cite this article as: MRS J. Nitride Semicond. Res. 4S1, G6.47 (1999) ABSTRACT The dissociation channels of two prominent bound exciton complexes in wurtzite GaN thin films are determined via an extensive temperature dependent photoluminescence study. The shallow donor bound exciton dissociation at low temperatures (T ≤ 50 K) is found to be dominated by the release of a free exciton with thermal activation energy consistent with the exciton localization energy. At higher temperatures a second dissociation channel with activation energy EA = 28 ± 2 meV is observed. The dissociation of a bound exciton complex with exciton localization energy EXloc = 11.7 meV is also dominated by the release of a free exciton. In contrast to previous studies evidence is presented against the hypothesis of this emission being due to the exciton bound to an ionized donor. We find that it originates most likely from an exciton bound to a neutral acceptor. INTRODUCTION Recent progress in the epitaxial growth of high quality GaN materials has permitted the observation of new photoluminescence (PL) emissions. Although some of these new transitions have been positively identified,1,2 broad PL linewidths preclude the definitive identification of other emissions. A bound exciton emission located ~12 meV below the free exciton is an example of such emission. This emission has been identified as a neutral acceptor-bound exciton (A0,X)3,4 or a neutral donor-bound exciton (D0,X)5 and more recently was assigned to an ionized donor-bound exciton (D+,X).6,7 The identification of the various emissions in GaN is essential to understanding and improving device performance via better dopants and more efficient luminescence. The temperature dependence of the PL intensity of a bound exciton complex can be used to identify the kinetics of its thermal dissociation, and thus to provide a valuable insight into the origin of this complex. The main channel of thermal decay is the one with the least activation energy, EA. In the case of a neutral donor-bound exciton complex in GaN the exciton delocalization from the neutral donor (EXloc ~ 6 meV) is likely to be the minimum-
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energy dissociation channel of that complex. Temperature dependent photoluminescence studies have been employed previously to investigate neutral donor-bound exciton emissions in GaN and other materials
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