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A free-standing GaN wafer was fabricated by depositing a GaN buffer that induced the formation of pits (hereafter, pit-inducing GaN buffer) on a low-temperature-grown GaN buffer on the sapphire substrate. A high-temperature-grown GaN layer was grown on the pit-inducing GaN buffer that induced the formation of pits on the high-temperature-grown GaN layer. The pit-inducing buffer suppresses crack formation in the thick GaN film thereby releasing growth stress. Thermal stress in GaN on a sapphire system is also discussed on the basis of calculations utilizing a bilayer model. We have succeeded in the fabrication of a nearly 4-in.-diameter free-standing GaN thick wafer with a pit-inducing GaN buffer by one-stop hydride vapor phase epitaxy, which will lead to a low-cost fabrication of free-standing GaN wafers.

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Five electron traps were detected successfully in heavily Si-doped GaAs and AlxGa1−xAs of low Al content with a Si concentration of above 1×1019 cm−3 using deep level transient spectroscopy. The junctions were grown by liquid phase epitaxy and were strongly compensated. The traps were investigated for functions of the Si concentration and the AlAs mole fraction. The traps are discussed in terms using their spectra and concentration as opposed to the previous results which used point defects in the GaAs and AlGaAs. The traps show distinctive features, which can be attributed to strongly Si-compensated crystals. Three traps among them were confirmed to be DX centers.

High-quality ZnS epitaxial J-ayers were grown on GaP substrates at a growth temperature higher than 200oC by ]-ow-pressure MOCVD technique. Undoped ZnS electrj_ca1 resistlvity was as high as an insul-ator. Aluminum doping of about 10 ppm lowers resi-stivity to around 104 CIcm. , Film thickness controll-ability is very good for this low-pressure ZnS growth. A homoepitaxial MIS structure, usihg undoped MOCVD-ZnS for an i-nsulaLor, has been revealed to have higher emission efficiency and reproducibility compared to a heterostructure MIS. This successful-trial has resulted in a promising procedure to obtain MIS ZnS Blue LEDs on GaP substrate by ]-ow-pressure MocvD technique.

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