Growth of a GaN overlayer with low threading dislocation density using stacking faults

We have studied the effects of the trimethylgallium (TMGa) flow rate for the GaN buffer layer on the optical and structural quality and of the stacking faults on the dislocation density. From low-temperature photoluminescence (PL) measurements, a GaN overlayer grown on a buffer layer with a TMGa flow rate of 80 mu mol/min shows a weak yellow-band emission at 2.2 eV, which is related with threading dislocations from transmission electron microscopy (TEM) images. As the TMGa flow rate is increased, the threading dislocation density rapidly decreases, and the number of stacking faults in the GaN overlayer increases. Also, the total threading dislocation density for the optimum buffer layer has a very low value of 1 x 10(8) cm(-2) due to the interaction of stacking faults with the vertical threading dislocations and the bending of threading dislocations near the stacking faults. High-resolution X-ray diffraction (HRXRD) results show that a high density of stacking faults correlates with compressive strain in the GaN overlayer at growth.