ABSTRACT
Sapphire has been the commonly used substrate material for the growth of the h-GaN films. Due to the large lattice-mismatch and difference in the thermal expansion coefficient, the GaN epitaxial layer contains a large density of threading dislocations (109-1010 cm"2) [1] and a large thermal stress [2]. Recently, the growth of h-GaN films on GaAs (111) substrates has attracted much attention [3,4], because the difference in the thermal expansion coefficients between GaAs and GaN is less than those with other materials as shown in Fig.l. Further, GaAs crystal is easy to cleave and to etch and form ohmic contacts. There are a few reports on the growth of GaN fimls on GaAs (111) substrates. Naoyuki et al. reported the growth of h-GaN by metalorganic hydrogen chloride vapor phase epitaxy (MOH-VPE) using double GaN buffer layers on GaAs (111 )B substrates [3]. The room-temperature photoluminescence (PL) spectra exhibited a strong peak at approximately 361.5 nm. Hasegawa et al. [4] reported that h-GaN with smooth surface could be grown on the GaAs (111) substrate at a growth
temperatures as high as 1000 °C by hydrogen chloride vapor phase epitaxy (HVPE) using intermediate GaN layer. However, the structural properties of GaN grown on GaAs (lll)B substrates have not yet been reported. It is interesting to compare them with those properties of GaN epilayer grown on other substrate, such as, sapphire or 6H-SiC.
