Well-width-dependent carrier lifetime in AlGaN∕AlGaN quantum wells

Abstract

A set of ${\mathrm{Al}}_{0.35}{\mathrm{Ga}}_{0.65}\mathrm{N}∕{\mathrm{Al}}_{0.49}{\mathrm{Ga}}_{0.51}\mathrm{N}$ multiple quantum wells (MQWs) with fixed barrier width and well widths varying from $1.65\text{to}5.0\mathrm{nm}$ has been grown by metal-organic chemical vapor deposition. Carrier dynamics in the MQWs were studied using time-resolved photoluminescence (PL) spectroscopy and light-induced transient grating (four wave mixing) technique. The authors observed that the lifetime of nonequilibrium carriers (excitons) increases with decreasing well width and interpreted the effect by stronger localization preventing their migration to nonradiative recombination centers. Meanwhile the radiative decay time is also influenced by screening of the built-in electric field, which spatially separates the electrons and holes. It is shown that this effect affects the initial part of PL intensity decay after pulsed excitation. It becomes more pronounced with increase in the initial carrier density but saturates when the carrier density is high enough to completely screen the built-in electric field. The screening effect on PL decay is stronger in wider quantum wells.