Well-width dependence of the quantum efficiencies of GaN/AlxGa1-xN multiple quantum wells

A set of GaN/AlxGa1-xN(x approximate to 0.2) multiple quantum wells (MQWs) with well widths, L-w, varying from 6 to 48 Angstrom has been grown by metalorganic chemical vapor deposition under the optimal GaN-like growth conditions. Picosecond time-resolved photoluminescence spectroscopy has been employed to probe the well-width dependence of the quantum efficiencies (QE) of these MQWs. Our results have shown that these GaN/AlGaN MQW structures exhibit negligibly small piezoelectric effects and hence enhanced QE. Furthermore, GaN/AlxGa1-xN MQWs with L-w between 12 and 42 Angstrom were observed to provide the highest QE, which can be attributed to the reduced nonradiative recombination rate as well as the improved quantum-well quality. The decreased QE in GaN/AlxGa1-xN MQWs with L-w< 12 Angstrom is due to the enhanced carrier leakage to the underlying GaN epilayers, while the decreased QE in MQWs with L-w> 42 Angstrom is associated with an increased nonradiative recombination rate as L-w approaching the critical thickness of MQWs. The implications of our results on device applications are also discussed. (C) 2000 American Institute of Physics. [S0003-6951(00)04921-4].