Compound-source Molecular Beam Epitaxy of GaN on Si at Low Temperature Using GaN Powder and Ammonia as Sources
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0955-I07-23
Compound-source Molecular Beam Epitaxy of GaN on Si at Low Temperature Using GaN Powder and Ammonia as Sources
Tohru Honda, Masaru Sawada, Hiromi Yamamoto, and Masashi Sawadaishi Department of Electronic Engineering, Kogakuin University, 2665-1 Nakano-machi, Hachiohji, Tokyo, 192-0015, Japan
ABSTRACT Low-temperature growth of GaN is very attracting for the application to light emitting devices grown on Si substrates because it prevents the melt-back reaction between Ga and Si substrates. The low-temperature growth of GaN by compound-source molecular beam epitaxy (CS-MBE) has been reported. In the previous report, GaN powders were used as a source and no additional nitrogen source was introduced during the growth. At present, its growth mechanism is unclear. In this paper, CS-MBE of GaN layers using GaN and ammonia as sources is discussed. Especially, the reduction of excess Ga in GaN layers by introducing ammonia supply is discussed based on their refraction high-energy electron diffraction (RHEED) patterns and x-ray photoelectron spectroscopy (XPS) spectra. 1. Introduction GaN-based light-emitting devices grown on Si substrates are very attractive for the cost-effective fabrication. Generally, GaN growth requires high substrate temperatures around 1000 °C. Low-temperature growth of GaN is very attracting for the application to light-emitting devices because it prevents the melt-back reaction between Ga and Si substrates [1]. The low –temperature growth is also effective for the reduction of surface cracks and residual strain in the epitaxial layers due to the difference of thermal expansion coefficients. On the other hand, molecular beam epitaxy (MBE) of GaN is one of the suitable techniques for the fabrication of GaN-based light-emitting devices. In the case of metal-organic vapor phase epitaxy (MOVPE), there are premature reactions such as trimethylaluminum (TMAl) and ammonia, which lead to irregular thickness and composition of Al(Ga)N layers. In the case of MBE growth, we can avoid those premature reactions. The low-temperature growth of GaN by compound-source molecular beam epitaxy (CS-MBE) has been reported [2]. In the previous report, GaN powders were used as a source and no additional nitrogen source was introduced during the growth. Although GaN layers were grown at the low temperature of 450 °C by CS-MBE, their conditions were Ga-rich. At present, detailed growth mechanism of the CS-MBE is unclear. In this study, CS-MBE of GaN layers using GaN powder and ammonia as sources is reported. In particular, the reduction of excess Ga in GaN layers by introducing ammonia supply is
Fig. 1 Schematic drawing of CS-MBE system.
Fig. 2 Growth rate and relative oxygen concentration of GaN layers as functions of ammonia flow rate.
discussed. 2. Experiments GaN powder and ammonia were adopted for GaN growth by CS-MBE, whose schematics are shown in Fig. 1. The GaN powder, which was synthesized from gallium metal and ammonia, was annealed in vacuum at 800 °C up to 10h [3]. (0001)6H-SiC and (111)Si were us
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