A study was made of the effect of the trimethylgallium flow rate, in a GaN buffer layer, upon structural quality. Low-temperature photoluminescence measurements were made of a GaN overlayer which was grown onto a buffer layer by using a trimethylgallium flow rate of 80μmol/min. These revealed an intense donor-acceptor pair transition peak at 3.27eV, and a weak yellow band emission at 2.2eV. These were related to stacking faults and threading dislocations, respectively. As the trimethylgallium flow rate for the GaN buffer was increased, the threading dislocation density decreased rapidly and the stacking fault number density increased in the GaN overlayers. The total threading dislocation density for an optimum buffer layer was only 108/cm2. This was attributed to the interaction of stacking faults with vertical threading dislocations, and to the bending of threading dislocations near to the stacking faults. High-resolution X-ray diffraction results showed that a high density of stacking faults was related to the compressive strain of the GaN overlayer at the growth temperature.

Effect of Buffer Layers and Stacking Faults on the Reduction of Threading Dislocation Density in GaN Overlayers Grown by Metalorganic Chemical Vapour Deposition. H.K.Cho, J.Y.Lee, K.S.Kim, G.M.Yang, J.H.Song, P.W.Yu: Journal of Applied Physics, 2001, 89[5], 2617-21