Optical properties of nonpolar (1(1)over-bar00) and semipolar (1(1)over-bar01) GaN grown by MOCVD on Si patterned substrates

Non-polar (1(1)over bar00) and semipolar (1(1)over bar01) GaN layers were grown on (112) and (001) Si substrates, respectively, by metal-organic chemical vapor deposition. In both cases, grooves aligned parallel to the < 110 > Si direction were formed by anisotropic wet etching to expose vertical {111}Si facets for growth initiation. The effect of growth conditions (substrate temperature, chamber pressure, ammonia and trimethylgallium flow rates) on the growth habits of GaN was studied. It was found that low pressure and low ammonia flow rate are beneficial for m-facet formation, while high ammonia flow rate promotes formation of (1(1)over bar01) facets. Steady-state and time-resolved photoluminescence measurements revealed that the optical quality of (1(1)over bar01) oriented GaN is comparable to that of c-plane GaN film grown on sapphire. The nonpolar (1(1)over bar00) GaN shows only weak emission and fast non-radiative recombination rate. The poor optical quality of the m-plane GaN can be explained by carbon incorporation during the growth under low pressure. Although further optimization of the growth conditions for better optical quality is required, preliminary results obtained for semipolar (1(1)over bar01)-oriented GaN are encouraging.