MOCVD growth of GaN‐based materials on ZnO substrates

The metalorganic chemical vapor deposition (MOCVD) growth of GaN based materials on ZnO substrates has numerous technical issues that need to be investigated and resolved. These include the thermal stability of ZnO, out‐diffusion of Zn/O from the ZnO into the epilayers, and H 2 back etching into the ZnO all of which can cause poor film quality. Cracks and pinholes were seen in the epilayers, leading to the epilayer peeling off. In this study, good quality InGaN films with a wide range of indium incorporation have been grown on (0001) ZnO substrates by MOCVD. No indium droplets and phase separation were observed even at high indium concentrations. The optical microscopy and field‐emission scanning electron microscopy revealed a mirror‐like InGaN surface with no evidence of indium droplets on the surface. Photoluminescence (PL) showed broad InGaN‐related emissions with peak energy lower than the calculated InGaN band gap, possibly due to Zn/O impurities diffused into InGaN from the ZnO substrate. More recently, Al 2 O 3 coated ZnO substrates have been employed for growth to limit Zn diffusion as well as assist epilayer growth. HRXRD result shows that a single crystal InGaN film has been successfully grown on an annealed Al 2 O 3 coated ZnO substrate. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)