Cathodoluminescence and field emission from GaN/MgAl ₂ O ₄ grown by metalorganic chemical vapor deposition: substrate-orientation dependence

GaN films with single-crystalline and polycrystalline structures were deposited by metalorganic chemical vapor deposition (MOCVD) on (111) and (100) MgAl2O4 substrates modified by chemical etching and thermal passivation. The oriented GaN films on the as-processed (111) MgAl2O4 substrate revealed broad visible emission band bands at 3.2 eV and a sharp luminescence peak centered at 1.8 eV in room temperature cathodoluminescence measurements, which can be attributed to the recombination of donor–acceptor pairs and GaN-related emission, respectively. Field emission (FE) measurements demonstrated that the oriented nanostructured 150 nm-thick GaN film on the as-processed (111) MgAl2O4 substrate has an ultralow turn-on-field of 4.29 V μm−1 at 10 nA cm−2 and a stable emission of 0.028 mA cm−2 with 5% current density fluctuation for 22 h without any degradation. Compared to GaN films on as-processed (100) MgAl2O4 substrate, the mechanism for the improved performance in optical and FE properties of the GaN film on as-processed (111) MgAl2O4 substrate has been investigated in detail.