We report on the growth of GaN in GSMBE using NH3 as nitrogen source. Special focus will be on the NH3 cracking, where we applied an On Surface Cracking technique (OSC). Using OSC we achieve photoluminescence linewidths as narrow as 5.5meV (5K) and mobilities of 220 cm2/Vs at room temperature.

This letter reports the successful growth of short period (ZnSe)4/CdSe4 strained layer superlattices on (100) GaAs surface by atomic layer epitaxy. The superlattice was characterized by x-ray diffraction and Raman scattering. Superlattice period was calculated from the satellite peaks and was in good agreement with the expected value. 2LO Raman scattering in resonance with the E1h exciton level was observed. Experimental exciton energy was compared with the one calculated in a finite-square-well model. A Raman line due to stimulated Raman scattering was also observed.

In this paper, Hydride Vapour Phase Epitaxy (HVPE) of GaN layers under reduced pressures is reported. First results show that the HVPE grown GaN layers exhibit excellent electrical, crystallographic and optical quality. By reducing the reactor pressure from 950 to 250 mbar, improvements in background doping (down to 2 Â 10 16 cm À3 ) and Hall mobility (up to 300 cm 2 /Vs) are observed. Experiments on MOVPE overgrowth on HVPE GaN layers show excellent results. Low temperature PL spectra of the overgrowth MOVPE layer reveal all three free exciton levels (FE A, FE B, FE C) without any visible bound excitons.

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