Quantum and transport lifetimes in optically induced GaN/AlGaN 2DEGs grown on bulk GaN

A two-dimensional electron gas (2DEG) is absent in ultrapure GaN/Al_0.06Ga_0.94N heterostructures grown by molecular beam epitaxy on bulk GaN at 300 K and in the dark. However, such a 2DEG can be generated by UV illumination and persists at low temperature after blanking the light. Under steady UV illumination as well as under persistence conditions, pronounced quantum transport with Shubnikov–de Haas oscillations commencing below 2 T is observed. The low temperature 2DEG mobility amounts to only ∼20 000 cm²/V s, which is much lower than predicted for the dominant scattering mechanisms in GaN/AlGaN heterostructures grown on GaN with low threading dislocation density. A rather small ratio of the transport and quantum lifetimes τ_t/τ_q of ∼10 points at elastic scattering events limiting both the transport and quantum lifetimes.