Achieve high-quality GaN films on La0.3Sr1.7AlTaO6 (LSAT) substrates by low-temperature molecular beam epitaxy

The growth of c-plane GaN films on La0.3Sr1.7AlTaO6 (LSAT) (111) substrates has been carried out by molecular beam epitaxy (MBE) at various substrate temperatures. GaN grown at 750 degrees C shows poor crystallinity with an up to 8 nm thick interim layer between LSAT and GaN, mainly due to the severe interfacial reaction between the substrate and the film. On the contrary, an atomically abrupt interface has been observed when GaN was grown at a lower temperature of 500 degrees C. This low-temperature grown GaN exhibits high crystallinity with a very smooth surface and strong band-edge emission, which we attribute to the well-controlled oxygen atom evaporation from LSAT substrate surface thanks to the low temperature growth. On the one hand, it avoids the severe interfacial reaction that takes place in the case of high-temperature epitaxial growth; 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 LSAT. Considering the advantages of LSAT over sapphire, and the device-ready film quality of GaN achieved on LSAT, this work exhibits a promising future for high-performance light emitting diodes on this unconventional substrate.