Recombination Related to Two-Dimensional Electron Gas of Al_xGa_1−xN/GaN Single Heterostructures Studied with Picosecond Time-Resolved Photoluminescence

Abstract

Nearbandgap radiative recombination in undoped Al_xGa_1−xN/GaN (x = 0.28 to 0.35) single heterostructures grown by metalorganic chemical vapor deposition is investigated using picosecond time-resolved photoluminescence at 11K. Room temperature Hall effect measurements show both high sheet carrier concentrations (~1×10¹³ cm⁻²) and high mobilities (~1000 cm²/Vs), suggesting the formation of a two-dimensional electron gas (2DEG) at the heterointerface. The luminescence transient of the 3.481 eV emissions, which is usually assigned to donor-bound exciton emission of GaN, consists of an initial fast component and a slow second component. Samples with higher aluminum concentrations show broad luminescence peaks in the spectral range of 3.41—3.45 eV with long decay lifetimes over 1 ns. In addition, the below bandgap emissions saturate at high excitation power and shift toward lower energies with increasing time delay. The observed emissions are explained by the recombination processes involving the 2DEG at the heterointerface.