Characterization of Bulk, Polycrystalline Indium Nitride Grown At Sub-Atmospheric Pressures
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ABSTRACT Polycrystalline, wurtzitic indium nitride was synthesized by saturating indium metal with atomic nitrogen from a microwave plasma source. Plasma synthesis avoids the high equilibrium pressures required when molecular nitrogen is used as the nitrogen source. Two types of growth were observed: 1) small amounts of indium nitride crystallized from the melt during cooling and 2) hexagonal platelets formed adjacent to the In metal source on the crucible sides. The mechanism of this latter growth is not established, but may involve transport of indium as a liquid film. The crystals were characterized by electron diffraction, X-ray diffraction, elemental analysis, scanning electron microscopy, and Raman spectroscopy. Lattice parameter and Raman active phonon modes are reported and compared with calculations based on the full-potential linear muffin-tin orbital method (FP-LMTO). INTRODUCTION Of the 11I-V nitride wide band gap semiconductors, indium nitride has received the least attention. Indium nitride is also the most difficult to grow; the equilibrium vapor pressure of N2 over InN is higher than that over GaN and AIN [1]. Additionally, the In-N bond is the weakest among the
rn-V nitrides
[2]. High quality InN crystals are of inherent scientific interest. Also,
for obtaining blue light emission from nitride based structures, a significant amount of In (2040%) must be incorporated into GaN [3,4]. Efforts at bulk synthesis of InN have primarily been at high pressures because of the high equilibrium pressures of N 2. Successful synthesis of small crystallites (5-50 micron) has been achieved at an N2 pressure of 18-20 kbar and a temperature range of 700-900'C [5]. We have recently shown that GaN and InN can be synthesized at low pressures by use of atomic nitrogen, N, rather than molecular nitrogen, N2, to saturate gallium or indium with nitrogen [6,7,8]. Subsequently, similar results were obtained by Krukowski, et al., for InN [9]. In this paper we report on the growth of well-faceted bulk InN using nitrogen ECR and ball plasma configurations at sub-atmospheric pressures. Comparisons of measured lattice constants and optical phonon modes are made to theoretical calculations done using the fullpotential linear muffin-tin orbital method (FP-LMTO) [10]. EXPERIMENT/SYNTHESIS The pure indium shot was held in either an h-BN crucible for experiments without a bias voltage, or a machined, nitrided stainless steel crucible lined with nitrided molybdenum foil for experiments with bias. The reaction chamber was initially evacuated to a base pressure of 10-6 torr. In order to remove indium oxide or other impurities from the surface, the indium was independently heated from below while being exposed to a hydrogen plasma with 800 watts of 549
Mat. Res. Soc. Symp. Proc. Vol. 482 ©1998 Materials Research Society
microwave power at 20 torr for 30 minutes. Although the temperature at the bottom of the susceptor during this step was approximately 450'C, the actual temperature at the crucible was unknown as there is much additio
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