Cathodoluminescence and field emission from GaN/MgAl₂O 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) MgAl ₂O₄ 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.