GaN PN-Structures Grown by Hydride Vapor Phase Epitaxy
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ABSTRACT For the first time, GaN pn-junctions were fabricated by hydride vapor phase epitaxy. GaN pn-structures were grown directly on 6H-SiC substrates without any buffer layer. Undoped GaN layers were n-type with Nd-Na concentration ranged from IxI0 17 to 5x1018 cm-3. Magnesium was used as an acceptor to grow p-type GaN layers. Mg atomic concentration determined by secondary ion mass spectroscopy ranged from 5x10 19 to 5x10 20 cm3 . As-grown GaN layers doped with Mg were p-type, and p-type conductivity was improved by post-growth anneal. Mesa diodes with a vertical current flow geometry were formed by reactive ion etching. The position of the GaN pn-junction was determined by the electron beam induced current method. The electrical characteristics of the pn diodes were studied. Electroluminescence from the pn diodes was measured. INTRODUCTION Since the first report on single crystal GaN growth by hydride vapour phase epitaxy
(HVPE) by Maruska and Tietjen in 1969 [1], many important results have been achieved on epitaxial growth, doping and investigation of III-V nitrides [2]. The great breakthrough was done in 1989 when Akasaki and co-workers reported first p-type GaN [3]. The subsequent progress in GaN growth and doping has paved the way for the development of a variety of GaN-based semiconductor devices. It must be emphasised that progress in III-V nitride device fabrication was based on the development of metal organic chemical vapour deposition (MOCVD) and molecular beam epitaxy techniques. In spite of the fact that the HVPE method has been known to be more convenient for mass production because of its low cost and reproducibility, this method has been considered only as a technique for the deposition of thick GaN layers [4,5,6], not device structures. The poor crystal quality and high background carrier concentration (>1019 cm"3) of GaN layers grown by HVPE limited its device applications. In 1996, we reported on the HVPE growth of thin GaN layers. We indicated that they exhibited good structural quality and low background donor concentration [7]. The next step was the development of the HVPE growth technique for AIN and AlGaN layers, and AlGaN/GaN heterostructures [8,9]. In order to control thickness of III-V nitride layers in these heterostructures, the growth rate in the HVPE method was reduced to the value of 3 jtm/hr which is typical for MOCVD growth. The device quality of HVPE grown GaN 251 Mat. Res. Soc. Symp. Proc. Vol. 482 ©1998 Materials Research Society
layers has been proved by the fabrication of n-GaN/p-SiC pn diodes [10]. However, the main obstacle which restricted the application of the HVPE technique for GaN device fabrication was its inability to produce p-type GaN. In this paper, we report on the first p-type GaN grown by HVPE, and the characteristics of GaN pn-homojunctions fabricated by the HVPE method. EXPERIMENT 6H-SiC/n-GaN/p-GaN epitaxial structures were grown in two stages by the HVPE method. The first stage involved the growth of GaN undoped layers with n-type conductivity. 6H-Si
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