Physical Properties of Bulk GaN Crystals Grown by HVPE
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Internet Journal o f
Nitride S emiconductor Research
Volume 2, Article 39
Physical Properties of Bulk GaN Crystals Grown by HVPE Yu.V. Melnik PhysTech WBG Research Group, Ioffe Institute and Crystal Growth Research Center K.V. Vassilevski, I.P. Nikitina, A.I. Babanin PhysTech WBG Research Group, Ioffe Institute V. Yu. Davydov Ioffe Physical-Technical Institute V.A. Dmitriev PhysTech WBG Research Group, Ioffe Institute and Materials Science Research Center of Excellence, School of Engineering, Howard University This article was received on June 11, 1997 and accepted on September 17, 1997.
Abstract Free standing GaN platelets were fabricated by hydride vapor phase epitaxy (HVPE). The platelets having a current maximum size of 7x6x0.1 mm3 were obtained by HVPE growth of ~100 µm thick GaN layers on SiC substrates and subsequent removal of the substrates by reactive ion etching (RIE). Surface of the GaN platelets was characterized by reflectance high energy election diffraction (RHEED), and Auger electron spectroscopy (AES). Crystal structure and optical properties of the platelets were studied by x-ray diffraction and photoluminescence (PL), respectively. Raman spectroscopy was also applied for material characterization. Residual strain was detected in the crystals. The stress was eliminated by high temperature anneal.
1. Introduction The Group III-V nitrides (GaN, AlN, InN) are the prominent materials for blue-green and UV light emitting diodes (LEDs), laser diodes (LDs), and high frequency, high power transistors. High brightness blue and green III-V nitride LEDs have been commercialized [1], and prototype LDs have been demonstrated [2]. Despite a rapid progress in the field, a number of basic scientific and technological issues remain to be unsolved. One of the most severe problem is the lack of a suitable substrate material on which lattice-matched nitride films may be grown. The most widely used substrates for III-V nitride epitaxy are sapphire [3] and silicon carbide [4]. However, a poor lattice match and difference of thermal expansion coefficients for these substrates usually lead to the formation of threading defects, high dislocation density, and residual strains in the epitaxial layers. These defects may affect both electrical and optical properties of the material and devices. If available, bulk GaN substrates would be a better choice. Previously, GaN free standing platelets have been fabricated by hydride vapor phase epitaxy (HVPE) using sapphire substrates [5]. We believe that SiC is a better substrate for GaN because of smaller lattice and thermal mismatch. It has been shown that HVPE method insures high quality GaN deposition on SiC substrates providing material with dislocation density in a low 108 cm-2 range. Thin (~1 µm) GaN layers grown by HVPE on SiC have been used as substrates for Molecular Beam Epitaxy of GaN [6]. In this paper, we report the fabrication of free standing GaN platelets by HVPE of ~100 µm thick GaN layers on SiC substrates and subsequent removal of the substrates by reactive
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