Effects of growth interruption on the structural and optical properties of GaN self-assembled quantum dots
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Y4.1.1
Effects of growth interruption on the structural and optical properties of GaN self-assembled quantum dots K. Hoshino, S. Kako, and Y. Arakawa Research Center for Advanced Science and Technology, and Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
ABSTRACT We report the effects of thermal annealing and growth interruption on the formation of GaN self-assembled quantum dots (QDs) grown by low-pressure metalorganic chemical vapor deposition (MOCVD). For the uncapped QD structures, atomic force microscopy (AFM) analysis shows that the density of the QDs rapidly increases and then decreases with increasing the annealing time. This is due to the combined effect of the QD formation process and the ripening process. The size of the QDs increases with increasing the annealing time. We have also investigated the photoluminescence (PL) property of the AlN capped QD structures with different growth interruption times. The PL from the QDs showed a red-shift with increasing the growth interruption time. In contrast, the PL from the wetting layer (WL) shows a blue-shift. These results indicate that the formation of the QDs is proceeding at the expense of the WL, which is consistent with the AFM analysis of the thermal annealing effect. These results show that the growth interruption plays an important role in the formation of the QDs.
INTRODUCTION QD structures are systems of great interest for the development of new devices. Lasers with QDs embedded in the active layer are predicted to improve the characteristics of lasers, such as suppression of temperature dependence of the threshold current [1], a reduced threshold current density, and a reduced total threshold current [2,3]. In nitride semiconductors, the use of QDs is more effective, since the zero-dimensional electronic states in the QDs play an essential role for improving threshold current characteristics particularly in wide bandgap semiconductors [4, 5]. Moreover the QD structure contains no dislocations, therefore it is expected to impart higher efficiency since carriers confined inside the QDs are not trapped at nonradiative recombination centers formed by dislocations outside [6, 7]. The growth of GaN-based QDs has already been investigated by several groups. GaN self-assembled QDs on an AlN layer by Stranski-Krastanow (SK) growth mode have been demonstrated using molecular beam epitaxy (MBE) [8] or MOCVD [9]. The growth of GaN self-assembled QDs on an AlGaN layer was reported using “antisurfactants” by MOCVD [10] and the stimulated emission from these QDs was also reported [11]. As another way to fabricate GaN QDs, the selective growth method was proposed [12].
Y4.1.2
In this paper, we report the growth of GaN self-assembled QDs grown by low-pressure MOCVD. The effect of thermal treatment on the formation of GaN QDs has been systematically investigated. We have also investigated the effect of growth interruption on the PL property of GaN QDs.
MOCVD GROWTH OF GaN SELF-ASSEMBLED QDs GaN self-assembled
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