Time-resolved photoluminescence of a two-dimensional electron gas in an Al_0.2Ga_0.8N/GaN heterostructure fabricated on ammonothermal GaN substrates

A characteristic photoluminescence signal is identified for a two-dimensional electron gas (2DEG) confined at an Al_0.2Ga _0.8N/GaN heterointerface fabricated on an ammonothermal GaN (AT-GaN) substrate. The use of a gas-phase synthesized NH₄Cl acidic mineralizer reduced oxygen contamination in AT-GaN by two orders of magnitude, and metalorganic vapor phase epitaxy of atomically smooth, coherent AlGaN/GaN heterostructures was realized. The emission originating from the 2DEG is interpreted using self-consistent Schrödinger-Poisson calculation, taking the interfacial immobile charge due to polarization discontinuity into account. The initial decay time at low temperature was close to that of the bulk free excitons, reflecting the lifetime of photoexcited holes.