Effect of buffer layers and stacking faults on the reduction of threading dislocation density in GaN overlayers grown by metalorganic chemical vapor deposition

We have studied the effect of the trimethylgallium (TMGa) flow rate in the GaN buffer layer on the optical and structural quality. From low temperatur e photoluminescence measurements, a GaN overlayer grown on a buffer layer w ith the TMGa flow rate of 80 mu mol/min shows the intense donor-acceptor pa ir transition peak at 3.27 eV and the weak yellow band emission at 2.2 eV, which are related with stacking faults and threading dislocations from tran smission electron microscopy images, respectively. As the TMGa flow rate of the GaN buffer increases, the threading dislocation density rapidly decrea sed and stacking faults increased in the GaN overlayers. Also, a total thre ading dislocation density at the optimum condition of the buffer layer is t he very low 1x10(8) cm(-2), which is due to the interaction of stacking fau lts with the vertical threading dislocations and the bending of threading d islocations near the stacking faults. High-resolution x-ray diffraction res ults show that a high density of stacking faults is correlated with the com pressive strain of a GaN overlayer at the growth temperature. (C) 2001 Amer ican Institute of Physics.