The initial growth conditions of a 100 nm thick GaN layer and Mg-surfactant on the quality of the GaN epilayer grown on a 6H-SiC substrate by metal-organic vapor phase epitaxy have been investigated in this research. Experimental results have shown that a high V/III ratio and the initially low growth rate of the GaN layer are favorable for two-dimension growth and surface morphology of GaN and the formation of a smoother growth surface. Mg-surfactant occurring during GaN growth can reduce the dislocations density of the GaN epilayer but increase the surface RMS, which are attributed to the change of growth mode.
Non-polar a-plane (11 20) GaN films have been grown on r-plane (1 102) sapphire substrates by metal organic chemical vapour deposition. The influences of V/III ratio on the species diffusion anisotropy of a-plane GaN films were investigated by scanning electron microscopy, cathodoluminescence and high-resolution x-ray diffraction measurements. The anisotropy of a-plane GaN films may result from the different migration length of adatoms along two in-plane directions. V/III ratio has an effect on the growth rates of different facets and crystal quality. The stripe feature morphology was obviously observed in the film with a high V/III ratio because of the slow growth rate along the [1 100] direction. When the V/III ratio increased from 1000 to 6000, the in-plane crystal quality anisotropy was decreased due to the weakened predominance in migration length of gallium adatoms.
GaN-based laser diodes (LDs) with 399 nm wavelength are grown on sapphire substrates by metal organic chemical vapour deposition (MOCVD). Electroluminescence spectra of the fabricated LDs show that the LDs from some grown wafers failed to emit laser. The SEM and XRD results show the similar surface morphology and interface qualities of multi quantum wells (MQWs) and super-lattices between LDs that succeed and fail to emit laser. However, the cathodoluminescence (CL) measurements reveal a kind of optical defect rather than structural defect in un-emitted LDs. Further depth-dependent CL imaging observation indicates that such optical defects originate from the MQWs to the surface of LDs as a non-irradiative recombination centre that should cause the failure of laser emitting of LDs.
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