The role of growth rates and buffer layer structures for quality improvement of cubic GaN grown on GaAs

Cubic GaN (c-GaN) layers are gr own on GaAs(001) substrates by metalorpanic vapor phase epitaxy. To attain high-quality c-GaN, we investigate growth conditions and buffer layer structures. It is found that by increasing the growth rate from 0.35 to 1.05 mu m/h, the growth temperature region where the c-GaN composition reaches its maximum (90%) is shifted from 700-800 degrees C to 850-900 degrees C. Regarding the film properties, excitonic emission and high resistivity are realized with the faster growth rate. Subsequently, the c-GaN composition is improved by the use of a double buffer layer (DBL) structure instead of the conventional single buffer layer structure without degrading the achieved optical and electrical properties. The DBL structure preserves a relatively high c-GaN composition even in thick layers.