Double pendeo-epitaxial growth of GaN films with low density of threading dislocation
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Double pendeo-epitaxial growth of GaN films with low density of threading dislocation Y. K. Hong1, H. S. Jung1, C-H. Hong1*, M.H. Kim2 and S-J. Leem2 1
Dept. of Semiconductor Science and Technology
& Semiconductor Physics Research Center, Chonbuk National University Duckjin-Dong, Duckjin-ku, Chonju 561-756, Korea 2
OE Team, Device & Materials Laboratory
LG Electronics Institute of Technology, Seoul 137-724, Korea
ABSTRACT A double pendeo-epitaxy technique for growing uniformly GaN films with low defect density over the entire surface of a substrate has been achieved by metalorganic chemical vapor deposition(MOCVD). The structural properties of the first pendeo-epitaxial layers were optimized with the ratio of the lateral to the vertical growth rate, which is strongly affected by the growth temperature and the TMGa flow rate. The second pendeo-epitaxial growth was performed on the first regrown layers after removing a high defective region originating from underlying GaN seed layer. From the analysis of atomic force microscopy(AFM) images, the termination of surface steps by threading dislocations were not observed at the second regrown GaN layers. This result implies that a very low density of threading dislocation exists on the GaN surface. Cathodoluminescence(CL) results showed a strong band-edge emission from the all regrown regions. INTRODUCTION The lateral epitaxial overgrowth(LEO) technique has been received much attention since the development of InGaN blue laser diodes grown on an LEO GaN substrate[1]. Significant progress in reduction of defect density in GaN overgrown layers on a dielectric masked area was achieved using this technique[2-6]. For the most part research has been focused on increasing the lateral overgrown regions and reducing crystallographic tilts with optimized growth conditions. Recently, the pendeo-epitaxial(PE) growth, which is a new approach of LEO technique, has been developed by employing four-to-five times larger lateral growth rates of the regrown GaN from sidewalls of rectangular stripes compared to that of conventional LEO-GaN[7-10]. However, slight crystallographic tilt in the coalesced regions was occurred in the PE-GaN layers with the use of a mask[11]. In the case of those GaN layers without a mask, high defect densities in vertical growth region originating from (0001) direction of GaN template layer were found. Our recent report shows that isoelectronic Indoping, which can enhance vacancy trapping and then bend or terminate the dislocation in I3.21.1
the grain boundary, reduces threading dislocation density in the vertical and the coalesced regions for the PE-GaN[12]. However, this is still believed to limit the performance of device. In this paper, we report on a double pendeo-epitaxy technique without a dielectric mask for growing uniformly GaN films with low defect density and no crystallographic tilt over the entire surface of a substrate. EXPERIMENTAL DETAILS The substrate layers were prepared via growth of a 2.0 µm to 2.5 µm thick GaN layers at 1130 °C on about
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