Nitridation of β-Ga2O3 to GaN in an atmosphere of NH3/Ar was investigated from the view points of kinetic results by thermogravimetric analysis (TGA) and microstructural observation. TGA and X-ray powder diffraction results showed that the nitridation of Ga2O3 to GaN starts at about 650°C and decomposition of GaN formed occurs from 870°C. Isothermal TGA results showed that the nitridation proceeds linearly with time at 800 – 1000°C. Microstructural observation of the samples nitrided at 800°C showed that fine GaN particles (∼50 nm size) deposit on surfaces of Ga2O3 particles at an early stage, and the deposits grow with progress of the nitridation.

We have investigated lattice structures of GaN and InGaN/GaN single-heterostructures (SH) and double-heterostructures (DH) by the reciprocal space mapping using X-ray diffraction technique from (0002) plane. For a single GaN layers, the transition of the film structure from grains with relatively independent orientation at about 0.3 μm followed by the coalescence at about 1 μm, to a uniform film with mosaic structure at 1.4 μm was clearly observed. For DH structure, ω-mode FWHMs both from InGaN (In composition approximately 7 %) and capping-GaN layers increased with increasing film thickness from 20 nm to 110 nm indicating the increased mosaic structure in the thick InGaN. We also observed the dislocation related to this increasing mosaic structure.

The growth of bulk GaN by sublimation method and a homoepitaxial growth by MOCVD are reported. A photo-pumped stimulated emission is obtained from a homoepitaxial layer. The source powder used as a source in the sublimation method is investigated in detail, and it is shown that the powder contains many kinds of compounds consisting mainly of gallium, nitrogen and hydrogen. Growth nucleation control is performed by partly covering an MOCVD-GaN or a scratched-sapphire (0001) by Si02. Hexagonal columns of the size of about 200 μm in diameter and about 200 μm in height are selectively and uniformly grown at the window sites. This technique enables the device processing of crystallites and also helps to increase crystal size by increasing growth time, since it prevents the nucleation of new crystallites which work as sink of the growing species.

The acceptor binding energy is calculated to find out the best acceptor impurity in InN, GaN and AlN. Be is predicted to be the shallowest acceptor and the next are Mg and Zn. Group IV elements such as C or Si are very deep. Band lineup is calculated to be ΔEc : ΔEv = 2.1 eV : 0.76 eV = 0.73 : 0.27 = 2.8 : 1 for GaN/AlN and ΔEc : ΔEv = 0.88 eV : 0.66 eV = 0.57 : 0.43 = 1.3 : 1 for GaN/InN. GaN is grown on GaAs and GaP-coated Si substrate by MOCVD. GaAs intermediate layer gives better GaN compared to GaP intermediate layer. It is suggested that the lower bulk modulus of GaAs than that of GaP gives this difference.

The selective LPEE (liquid phase electro-epitaxy) growth of GaAs on GaAs-coated Si substrate prepared by MOCVD has been performed. Several attempts, the use of the insulator melt cap, lowering of the melt height and optimization of the stripe direction, have been tried to increase the lateral growth rate. Very wide (60 μm) lateral overgrowth on the SiO2 mask is obtained by making the stripe window in <010> and equivalent directions and by increasing the lateral current component in the LPEE. The GaAs layer laterally grown on the SiO2 has much less EPD (etch pit density) showing that the defect in the MOCVD-GaAs is blocked by the SiO2. The growth mechanism and the method of increasing the lateral growth rate are discussed.

UCGAS (undercut GaAs on Si) structures in which a part of the GaAs layer is separated from the Si substrate are newly developed to reduce both the thermal stress and the defect density. The stress distribution in the fabricated structures is evaluated by photoluminescence. Quite a good agreement between the measured and the analyzed distributions is obtained, and the stress in UCGAS is less than 1/10of that in planar GaAs on Si. The EPD (etch pit density) in UCGAS after thermal cycle annealing is also less than 1/10of that in the planar layer. UCGAS-LED is fabricated for the first time and tested. The UCGAS-LED emits in 7 meV shorter wavelength and has longer lifetime compared to the mesa-type LED fabricated from the same wafer.

GaAs has been successfully grown by LPE on partly covered (windowed) GaAs-on-Si substrates prepared by MBE. Almost dislocation-free layers were obtained in narrow stripe windows. The grown layers were characterized by photoluminescence and Hall effect measurement. The photoluminescence polarization indicated that a uniaxial tensile stress along the stripe direction is applied in the mesa stripe LPE layer while it is biaxial in the wide GaAs layer on Si. The stress relaxation in the direction perpendicular to the stripe is discussed.

GaAs and GaAsP with the entire compositional range are grow on Si using an intermediate layer of GaAsP strained superlattices to relax the lattice mismatch. The orientation of the overgrown GaAs layer is found to be determined by the direction of the off-angle of the Si (100) surface. The grown layers are characterized by photoluminescence, x-ray diffraction, electro reflectance and DLTS. GaAs/GaAlAs double heterostructure lasers and GaAsP visible LED's are fabricated on Si substrates. The structural and electronic properties of the grown layers and the device performances are reported in this paper.