Characteristics of FIELO-GaN Grown by Hydride Vapor Phase Epitaxy
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CHARACTERISTICS OF FIELO-GaN GROWN BY HYDRIDE VAPOR PHASE EPITAXY
Akira Usui, Haruo Sunakawa, Kenji Kobayashi, Heiji Watanabe and Masashi Mizuta System Devices and Fundamental Research, NEC Corporation 34 Miyukigaoka, Tsukuba Ibaraki 305-8501, Japan ABSTRACT The crystal quality of facet-initiated epitaxial lateral overgrowth (FIELO) -GaN, in particular, that in the vicinity of the GaN surface, is reported. It is shown that the surface smoothness of FIELO-GaN enables us to use it as an "epi-ready" substrate. The crystallinity of FIELO-GaN is evaluated by x-ray rocking curve (XRC) measurements. We indicate that the FWHM of XRC should be reduced with the decrease of the dislocation density. We previously reported that the dislocation behavior of FIELO-GaN causes the tilting of the c-axis in the overgrown regions. By using scanning reflection electron microscopy (SREM), however, we show that the tilting on the surface of thick FIELO-GaN was negligibly small. INTRODUCTION
The use of short-wavelength blue to violet coherent-light sources will enable us to double or triple the capacity of current optical storage systems. The InGaN materials system is the strongest candidate for a blue/violet coherent-light source [1]. Although this material system has strong potential for commercial use in blue/violet LDs, there are still inherent problems to be solved before mass-production of the devices will be practical. One of the significant problems is the lack of an appropriate high-quality substrate for growing a laser structure that is suitable for mass-production processes. Sapphire and SiC substrates are used presently. However, it is known that a large number of dislocations go through epitaxial layers from the interface between these substrates and epitaxial layers. The use of a lattice-matched substrate, such as GaN bulk crystal, is an ideal choice, but the preparation of large enough sized bulk GaN wafers of high crystal quality is still under development [2,3]. We studied the reduction of dislocation density in the epitaxial growth process. ELO, epitaxial lateral overgrowth, has been reported as an effective method for the reduction of dislocation density in other III-V compound semiconductors, such as GaP and GaAs [4,5]. However, no report had been published on GaN-ELO until our first paper in 1997, where we reported a FIELO (facet-initiated epitaxial lateral overgrowth) method for growing low-dislocation-density GaN layers by using hydride vapor phase epitaxy (HVPE) [6]. The dislocation density of 108 - to 109 cm-2 in the original GaN/sapphire hetero-interface was reduced to from 106- to 107 cm-2 by using this method. Crack-free GaN layers with mirror-like surfaces were successfully grown, even to a thickness of several hundred microns on a 2-inch-diameter sapphire substrate. The benefit of the ELO technique on InGaN MQW LD performance was first demonstrated by Nakamura et al in 1998 [7], where they reported the achievement of a long lifetime LD grown on a ELO-GaN substrate, as compared with a short-life time of 200
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