Optical properties and carrier dynamics of two-dimensional electrons in AlGaN/GaN single heterostructures

Abstract

We have investigated the optical properties and carrier dynamics of the two-dimensional electron gas (2DEG) in Al0.4Ga0.6N/GaN single heterostructures grown by metalorganic chemical vapor deposition by means of photoluminescence (PL), PL excitation, and time-resolved PL spectroscopy. Shubnikov-de Haas oscillations were clearly observed at 1.5 K, confirming the existence of a 2DEG. An additional 2DEG PL emission appeared at about 40 meV below the GaN band-edge emission and persisted up to about 100 K, while this peak disappeared when the top Al0.4Ga0.6N layer was removed by reactive ion etching. We observed abrupt PLE absorption at GaN band edge energy and approximately 50-ps delayed risetime compared to GaN and AlGaN emissions, indicating effective carrier transfer from the GaN flatband and AlGaN regions to the heterointerface. Even though the 2DEG emission is a spatially-indirect (slow) recombination, a fast decay component of similar to 0.2 ns is found to be dominant in 2DEG emission because of the fast exhaustion of photogenerated holes in GaN flatband region via spatially-direct (fast) GaN recombination. From the results, we explain the carrier generation, transfer, and recombination dynamics and the relationships between 2DEG, GaN, and Al0.4Ga0.6N emissions in undoped Al0.4Ga0.6N/GaN single heterostructures. (c) 2005 American Institute of Physics.