Growth and doping of cubic GaN films for optoelectronic devices

We discuss the conditions to be satisfied for the growth of cubic GaN films on GaAs(001) and Si(001) by plasma-assisted MBE. A stoichiometric group V/III flux ratio is required for single-phase growth, which is controlled via the surface reconstruction in real time by means of RHEED. While phase purity of cubic GaN-on-GaAs is induced by a well-defined orientation relationship, the growth on Si(001) often results in a phase transition due to the formation of amorphous SixNy inclusions at the GaN-on-Si interface, which act as nucleation centers for the growth of the hexagonal GaN phase. A suitable template, such as a thin GaAs or SiC insertion layer, prevents the formation of the SixNy inclusions. Cubic GaN grown under optimized conditions exhibit a narrow excitonic luminescence line at 3.272 eV at 5 K and high luminescence efficiency at room temperature. In addition, we discuss the origin of the n- type background doping in the as-grown layers and we present the new concept of codoping to achieve high p-type conductivity in GaN at room temperature.