Photoluminescence Properties Of Gan/AlGaN Multiple Quantum Well Microdisks

An array of microdisks with diameter of about 9 μm and spacing of 50 μm has been fabricated by dry etching from a 50 Å/50 Å GaN/AlxGa1-xN (x∼ 0.07) multiple quantum well (MQW) structure grown by reactive molecular beam epitaxy. The as-grown MQWs and the microdisk structures have been studied by picosecond time-resolved photoluminescence (PL) spectroscopy. PL emission spectra and decay dynamics were measured at various temperatures and pump intensities. With respect to the original MQWs, we observe strong enhancement of the transition intensity and lifetime for both the intrinsic and barrier transitions. The intrinsic transition is excitonic at low temperatures and exhibits an approximate 10 fold increase in both lifetime and PL intensity upon formation of the microdisks. The exciton transition magnitude diminishes rapidly with increased temperature however, while the enhanced lifetime shows little change. At room temperature the dominant GaN well transition is found to be band-to-band in nature as evidenced by effective band gap shrinkage and band-filling effects seen within the PL spectrum. The implications of our results to III-Nitride microdisk lasers are discussed.