AlN periodic multiple-layer structures grown by MOVPE for high quality buffer layer
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1202-I05-04
AlN periodic multilayer structures grown by MOVPE for high quality buffer layer. V. V. Kuryatkov, W. Feng, M. Pandikunta, D. Rosenbladt, B. Borisov, S. A. Nikishin and M. Holtz Nano Tech Center, Texas Tech University, Lubbock, Texas 79409, USA ABSTRACT High crystal quality crack-free AlN on sapphire was grown by low pressure metal organic vapor phase epitaxy (MOVPE). Growth experiments combine two recent approaches: the ammonia pulse-flow method and ammonia continuous-flow growth mode by varying the V/III ratio. The detailed aspects of MOVPE, employing the periodic multilayer approach at low, intermediate, and high temperatures are described. This method yields significant reduction of screw dislocation density and provides very smooth surface for thin AlN layers. INTRODUCTION Research into III-nitride semiconductors is important due to applications in photonics and electronics. The applications rely on the wide range of energy gaps possible with this material class. AlN is often used as a buffer layer which initiates epitaxy on various substrates and is transparent to ~ 210 nm, i.e., throughout the deep UV spectral region. Therefore, improvements in AlN growth are critical in obtaining high quality growth for devices based on wide-bandgap AlGaN [1]. In general, the difficulties of AlN growth are related to the low migration mobility of Al atoms and to significant pre-reaction of Al and ammonia. Khan et al. have proposed low pressure metalorganic pulsed atomic layer epitaxy (PALE) for the growth of AlN [2] on (0001) sapphire substrate. Imura et al. applied two- and three dimensional (2D and 3D) multi-growth mode, using various III-V ratios and high temperature (HT) to obtain AlN with low threading dislocation density [3]. Okada et al. have compared crystal quality of AlN grown at high temperature in multi-growth mode on low temperature (LT) and HT buffer layers [4] and found that combined LT buffer grown in continuous-flow mode and HT buffer grown in multi-growth mode yield better crystal perfection of crack-free thick AlN layers. Hirayama et al. have proposed the ammonia pulse-flow multilayer approach at onset of the low pressure metal organic vapor phase epitaxy (MOVPE) of HT AlN buffer layer [5]. In order to reduce the surface roughness of AlN grown in pulse-flow mode, they additionally used the highgrowth-rate continuous-flow mode for the following epitaxial layer grown at high temperature. Repetition of pulse- and continuous-flow mode yielded crack-free layers of thick AlN with smooth surfaces. Although the ammonia pulse-flow/continuous-flow (APF/ACF) approach at HT results in high crystal quality, the application of this method at LT for the growth of high quality thin AlN layers has not been thoroughly investigated. In this paper we summarize our systematic study of APF/ACF applied for the growth of LT and HT thin AlN buffer layers. The structural quality of the epilayers was characterized by X-ray rocking curve (XRC) analysis. The surface morphology of the epilayers was evaluated by atomic force
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