Time-resolved photoluminescence studies of InGaN/GaN multiple quantum wells
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Internet Journal o f
Nitride S emiconductor Research
Volume 2, Article 34
Time-resolved photoluminescence studies of InGaN/GaN multiple quantum wells J. Allègre, P. Lefebvre, S. Juillaguet, W. Knap, J. Camassel Groupe d'Etude des Semiconducteurs, GES-CNRS Q. Chen, M. A. Khan APA Optics Inc. This article was received on June 10, 1997 and accepted on September 15, 1997.
Abstract We report both cw and time resolved optical investigations performed on an InGaN/GaN multiple quantum well grown by MOVPE on -oriented sapphire substrate. At low temperature we find a strong "blue" luminescence band, of which energy position corresponds well with the wavelength of stimulated emission when excited with a nitrogen laser. We show that this PL band appears systematically red-shifted with respect to the QWs features, which supports a standard picture of fluctuations of the indium composition. Coming to the time-resolved data, we find at low temperature at least two "blue" band components which are both associated with long decay times (up to 4-5 ns at 8K). The decay time is temperature dependent and, when rising the temperature, the recombination rate increases. At room temperature, we reach typical values in the range ~100 to 500 ps.
1. Introduction In the present state of the GaN technology, manufacturing InGaN/GaN single quantum well (SQW) structures on sapphire substrates appears to be one of thr most promising issues for producing efficient blue LEDs (light emitting diodes) at reasonable cost (see for instance Ref. [1] and references therein). Using the same basic design, but multiple quantum wells (MQWs) stacks in the active region, room temperature operations of laser diodes (LDs) working under pulsed operation conditions have also been demonstrated [2] [3]. Despite this series of technological breakthroughs, it is useful to remember that (opposite to the more mature material systems based on GaInAsP, for instance) most details of the capture process which rules the spatial localization of the electron-hole pairs in the thick InGaN epitaxial layers and, a fortiori, in the moderately narrow (single or multiple) QWs are still far from being understood. Even the structural behavior of this peculiar alloy system sets problems. For instance, on thick 3-dimensional layers grown with a nominal 12% In composition, Harris et al. [4] reported energy-dependent recombination lifetimes. This suggested evidence of extrinsic localization effects, which were later confirmed by independent groups [1] [5]. These effects arise from uncontrolled fluctuations of the alloy composition. Direct correlation of these fluctuations with the change in PL emission energy under large excitation density (through the photorefractive effect) and with the change in PL linewidth with increasing alloy composition (through the piezoelectric effect) have been more recently suggested [6] [7]. In the case of single InGaN/GaN QWs, Jin Seo Im et al. [8] and C.-K. Sun et al [9] investigated the temperature dependence of the PL decay time. Similar to the simple e
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