Professor Robert Taylor

Abstract:

By using two-photon absorption spectroscopy we have performed time-integrated and time-resolved photolurninescence measurements on several coupled asymmetric GaN quantum discs, with embedded AlGaN barriers. We observe free-carrier screening, with an enhancement due to tunneling between the coupled quantum discs.

Abstract:

We present an investigation of free-carrier screening in coupled asymmetric GaN quantum discs with embedded AlGaN barriers using time-integrated and time-resolved micro-photoluminescence measurements, supported by three-dimensional multi-band k.p computational modeling. We observe that with increasing optical excitation the carrier lifetime decreases and emission energy blue-shifts. This originates from the screening of built-in piezo- and pyroelectric fields in the quantum discs by photo-generated free-carriers. Due to non-resonant tunneling of carriers from the smaller disc to the larger disc, free carrier screening is enhanced in the larger disc. The non-resonant tunneling was found to have a significant role in samples with a thin barrier, as the screening decreased with barrier thickness (i.e. decreased tunneling). Computational modeling was in good agreement with the experimental results.