Influence of Mis-Orientation of C-plane Sapphire Substrate on the Early Stages of MOCVD Growth of GaN Thin Films
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E3.40.1
Influence of Mis-Orientation of C-plane Sapphire Substrate on the Early Stages of MOCVD Growth of GaN Thin Films Seong-woo Kim1, Hideo Aida2 and Toshimasa Suzuki1 1 Nippon Institute of Technology, 4-1 Gakuendai, Miyashiro, Saitama, 345-8501, Japan 2 Namiki Precision Jewel Co., Ltd., 3-8-22 Shinden, Adachi-ku, Tokyo, 123-8511, Japan ABSTRACT We have studied the early stages of GaN growth to realize the growth mechanism of GaN thin films on mis-oriented sapphire substrates which affects the surface and crystal quality of GaN thin films. As the result, it was found that the larger mis-orientation angle helps the growth of the larger grain of GaN and leads to the earlier shift of growth mode from 3D to 2D. The AFM observation of closed-coalesced GaN thin films revealed the difference in the micro-step structures by the mis-orientation angle of sapphire substrate. The result of x-ray rocking curve as a function of mis-orientation angle well matched with the microstructure of GaN surface, indicating that the larger mis-orientation angle helps the column ordering of GaN crystals. INTRODUCTION GaN-based nitride semiconductor is one of the most promising candidates for blue lasers diodes (LDs), light-emitting diodes (LEDs), and high-power, high-frequency field-effect transistors (FETs) [1,2]. Epitaxial layers of III-N were typically grown on slightly mis-oriented sapphire substrate with low temperature GaN (LT-GaN) buffer layer by metal organic chemical vapor deposition (MOCVD). Some groups have reported the relationship between substrate mis-orinentation and the III-nitride epilayer growth [3-5]. We have also reported the effect of mis-orientation angle of c-plane sapphire substrate on surface morphology and crystal quality of 3µm thick GaN thin films grown by MOCVD [6]. With the atomic force microscope (AFM) observation, it was found that the smoothest surface of GaN film was obtained on around 0.15°-0.20° mis-oriented substrate. However, the surface roughness was increased in either case of less or excessive mis-orientation angle between 0.15°-0.20° range. On the other hand, the full width at half maximum (FWHM) of X-ray rocking curves (XRCs) for both GaN (002) and GaN (201) reflections were slightly improved as mis-orientation angle increased. These results revealed that the mis-orientation angle of sapphire substrate affects to a great extent to the growth mechanism of MOCVD grown GaN thin films. However, no one studied the growth mechanism in relation to the mis-orientation angle of sapphire substrate in detail. In this study, we observed the early stages of the epitaxial growth of GaN thin films grown by MOCVD on mis-oriented sapphire substrates to elucidate the growth mechanism. The elucidation of the growth mechanism of group-III nitride thin films is very important to obtain high quality epitaxial layers for devices and to develop highly efficient high frequency, high power/temperature electronic devices. EXPERIMENTAL
E3.40.2
We conducted the growth of undoped GaN thin films with LT-GaN layers using an
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