Barrier-width dependence of quantum efficiencies of GaN/AlxGa1-xN multiplequantum wells

We present the results of picosecond time-resolved photoluminescence (PL) m easurements for a set of 30 Angstrom well GaN/AlxGa1-xN (x similar to 0.2) multiple-quantum-well (MQW) structures with varying barrier widths L-B from 30 to 100 Angstrom, grown by metalorganic chemical-vapor deposition. The P L quantum efficiency and the recombination lifetime of these MQWs were obse rved to increase monotonously with an increase of the barrier width up to 8 0 Angstrom. These behaviors were explained by considering two distinct mech anisms that control the radiative recombination efficiencies in MQWs. When the barrier width is below the critical thickness, the nonradiative recombi nation rate increases with a decrease of the barrier width due to enhanced probabilities of the electron and hole wave functions at the interfaces as well as in the AlGaN barriers. On the other hand, the misfit dislocation de nsity increases as the barrier width approaches the critical thickness, whi ch can result in an enhanced nonradiative interface recombination rate. Our studies here have shown that the optimal GaN/AlGaN (x similar to 0.2) MQW structures for UV light-emitter applications are those with barrier widths ranging from 40 to 80 Angstrom. (C) 2000 American Institute of Physics. [S0 003-6951(00)00534-9].