Efficient Luminescence from {11.2} InGaN/GaN Quantum Wells
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Efficient Luminescence from {11.2} InGaN/GaN Quantum Wells Mitsuru Funato, Koji Nishizuka, and Yoichi Kawakami Kyoto University, Department of Electronic Science and Engineering, Kyoto 615-8510, Japan Yukio Narukawa and Takashi Mukai Nitride Semiconductor Research Laboratory, Nichia Corporation, Tokushima 774-8601, Japan
ABSTRACT InGaN/GaN multiple quantum wells (MQWs) with [0001], , and orientations have been fabricated by means of the re-growth technique on patterned GaN templates with striped geometry, normal planes of which are (0001) and {11.0}, on sapphire (0001) substrates. It was found that photoluminescence intensity of the {11.2} QW is the strongest among the three QWs, and its internal quantum efficiency was estimated to be as large as about 40% at room temperature. The radiative recombination lifetime of the {11.2} QW was about 0.39 ns at 14 K, which was 3.8 times shorter than that of conventional c-oriented QWs emitting at a similar wavelength. These findings are well explained by the high internal quantum efficiency in the {11.2} QW owing to the suppression of piezoelectric fields.
INTRODUCTION The internal quantum efficiency of light emitting diodes composed of InGaN/GaN quantum wells (QWs) is chiefly determined by two competitive factors, that is, exciton/carrier localization [1,2] and quantum confinement Stark effect (QCSE) caused by strong piezoelectric and spontaneous polarization in strained InGaN/GaN QWs [3,4]. The former improves the internal efficiency by suppressing the non-radiative processes, while the latter degrades it by preventing the radiative recombination. Therefore, it is quite important to reduce the QCSE to achieve higher emission efficiency. A clue for this can be found in Refs. [5] and [6], where the variation of the piezoelectric field as a function of the tilt of the c-axis was calculated and it is clearly shown that the piezoelectric field in strained InGaN on GaN can be zero at the tilt of 39° and 90°. This calculation suggests that InGaN/GaN QWs tilted by 39° or 90° can realize higher emission efficiency. The growth on non-polar planes, which forms 90° with (0001), has already been attempted [7], though it is generally difficult to grow polar materials such as GaN on non-polar substrates. On the other hand, a tilted {10.1} QW was fabricated in Ref. [6], but the QWs unexpectedly showed very weak luminescence due to the presence of a number of stacking faults. In this study, we propose the re-growth technique, where well-established and high quality c-oriented GaN is used as a seed. It is demonstrated that the growth on c-oriented GaN patterned with a stripe along the [1.00] direction forms (0001), {11.2}, and {11.0} facets and that the QW on the {11.2} facet involves weaker electric fields and has a higher luminescence efficiency, compared with conventional c-oriented InGaN/GaN QWs.
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re-growth
patterning
GaN sapphire(0001)
[0001]
(a)
[1.00]
[11.0]
(b)
(c) InGaN/GaN QW
Figure 1. Schematic of the formation process. (a) GaN template, (b) patterning b
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