GaN material system is gathering great interest from the viewpoints of its application to photonic and electronic devices. GaN is kwown tstrong photolouminescence (PL) emission in spite of high dislocatin density. This is quite different from other III-V semiconductors; for example, polycrystalline GaAs shows semi-insulating behavior and no PL. InGaN is usually used as an active layer in the photonic devices. However, InGaN is largely lattice-mismatched to GaN, which limits the thickness of InGaN. GaNP (GaNAs) alloy system is considered to show a large bandgap bowing and the same bandgap energy with small lattice-mismatch to GaN can be otained compared with InGaN. Recently, we have successfully grown GaNP and GaNAs by gas source MBE and confirmed the large bandgap bowing [1-3]. On the other hand, the gas source MBE growth of GaN on sapphire substrates with C-, A-, R- and M-planes showed only small difference in their PL properties [4]. As an extension of this ork, we have studied the growth of GaN layers on amporphous silica (SiO_2) substrates and observed strong PL emission [4-6].
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