Growth and electron microscopy study of GaN/MgAl2O4 heterostructures

Abstract

AbstractWe successfully grew Gallium nitride (GaN) films on MgAl2O4 (111) substrates using low temperature pulsed laser deposition (PLD). X‐ray diffraction rocking curves revealed the high quality of as‐grown GaN with its full width at half maximum (FWHM) along [0002] as small as 0.08°. Atomic force microscopy images showed very smooth surface of as‐grown GaN and indicated a two‐dimensional growth. High‐resolution transmission electron microscopy showed high structural perfection of GaN films. The crystalline structure for MgAl2O4 substrate from its body to its top part adjacent to GaN epitaxy kept constant, and the interface between GaN and MgAl2O4 was atomically abrupt. We attribute the high quality of as‐grown GaN films to the well‐controlled Mg atom evaporation from MgAl2O4 substrate surface owing to the application of low growth temperature in PLD: on the one hand, it avoids the severe interfacial reaction that is very likely to take place in conventional MOCVD or MBE growth, and hence makes the epitaxial growth possible; on the other hand, it conserves the crystalline structure of the substrate surface, and consequently takes good advantage of the small lattice mismatch between GaN and MgAl2O4.