Transport of Photoexcited Electron-Hole Plasma in GaN/AlGaN Quantum Well

We report spatially resolved photocurrent measurements showing transport of excitation on long distances in plane of a 6 nm GaN/$Al_{0.1}Ga_{0.9}N$ quantum well. The strong field present in nitrides (due to large spontaneous and piezoelectric polarizations) leads to lower recombination rates of electrons and holes, so in the case of electron-hole pairs excited by light, relatively long-lived electron-hole plasma could be generated. In the case of the investigated quantum well, lifetime of few μs was expected. The thermal measurements showed that barriers were low enough, so all excited carriers could reach the electrode (thermal activation energy of 0.11 eV was found). The diffusion length for unbiased structure was about 40 μm. It was observed that the charge transport could be clearly accelerated by bias. In the biased quantum well, the transport range was of the order of 100 μm under both positive and negative bias. The reported effect of long transport range is very important for electronic devices made on the GaN/AlGaN structures.