Luminescence characterizations of freestanding bulk single crystalline aluminum nitride towards optoelectronic application

Herein, freestanding wurtzite aluminum nitride (AlN) bulk single crystals (BSCs) were massively grown on a tungsten substrate using a two-heater physical vapor transport (th-PVT) method. The growth was along the c-axis of the hexagonal lattice with the crystal scales in the millimeter level. Cathodoluminescence (CL) measurement was performed on the AlN BSCs. The CL spectra showed both near band edge emission at 6.02 eV and defect-related emissions at around 4.60 eV (VAl) and 3.30 eV (V-Al-O complex). Moreover, an electroluminescence (EL) device with a sandwich structure of Au-AlN-W was fabricated and characterized. This EL device demonstrated an asymmetric current-voltage curve and white light luminescence with high color quality under high bias. They were attributed to different non-ohmic contacts at the metalsemiconductor interfaces and intrinsic defect-related energy states. This study aims at the pioneering exploration of the application of freestanding AlN BSCs in optoelectronic devices.