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 meta lorganic chemical vapor deposition under the optimal GaN-like growth condit ions. Picosecond time-resolved photoluminescence spectroscopy has been empl oyed to probe the well-width dependence of the quantum efficiencies (QE) of these MQWs. Our results have shown that these GaN/AlGaN MQW structures exh ibit negligibly small piezoelectric effects and hence enhanced QE. Furtherm ore, GaN/AlxGa1-xN MQWs with L-w between 12 and 42 Angstrom were observed t o provide the highest QE, which can be attributed to the reduced nonradiati ve recombination rate as well as the improved quantum-well quality. The dec reased QE in GaN/AlxGa1-xN MQWs with L-w< 12 Angstrom is due to the enhance d carrier leakage to the underlying GaN epilayers, while the decreased QE i n MQWs with L-w> 42 Angstrom is associated with an increased nonradiative r ecombination rate as L-w approaching the critical thickness of MQWs. The im plications of our results on device applications are also discussed. (C) 20 00 American Institute of Physics. [S0003-6951(00)04921-4].