Time resolved photoluminescence study of Si modulation doped GaN/Al0.07Ga0.93N multiple quantum wells

Abstract

AbstractThe effects of the Si doping level on the recombination dynamics and carrier (exciton) localization in modulation doped GaN/Al0.07Ga0.93N multiple‐quantum‐well (MQW) structures were studied by means of photoluminescence (PL) and time‐resolved PL measurements. All samples with different doping levels show a QW emission which is blue shifted with respect to the 3.48 eV PL peak from the GaN buffer layer. The decay time at the peak position remains nearly constant in the range of 320–420 ps at 2 K for all doping levels. For the undoped and low‐doped samples (3 × 1018 cm−3), which have less free electrons in the QWs, a non‐exponential PL decay behaviour at 2 K is attributed to localized exciton recombination. The more highly doped samples (5 × 1018 cm−3 to 1020 cm−3) show almost exponential decay curves at 2 K, suggesting the recombination of free electrons and localized holes. This localization effect appears even at high electron concentrations to cancel the expected lowering of the radiative lifetime with doping at 2 K; such a lowering is clearly observed at elevated temperatures for the highly doped samples, however. The internal polarization‐induced fields of the medium and highly‐doped samples are partly screened by the electrons originating from the doping in the barriers. Only the PL peak of the undoped and low‐doped samples shows a redshift with time delay, related to the photogenerated carriers. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)