Carrier escape mechanism in laterally correlated InAs sub-monolayer quantum dots using temperature dependent photoluminescence

Abstract

We have quantitatively investigated relative effects of photo-carrier escape mechanism upon the quenching of photoluminescence with temperature in an ensemble of embedded InAs sub-monolayer (SML) quantum dots by varying InAs SML coverage from 0.4 ML to 0.8 ML. The mutual interplay of carrier recombination and tunneling throughout the laterally coupled quantum dots for different InAs coverage have been established to determine the temperature dependent photoluminescence (TDPL) spectra. The respective characteristic life times were extracted from the individual TDPL spectra by fitting them with model carrier rate equation. The consequent enhancement of inter-dot tunnel strength with respect to the carrier recombination rate with increasing InAs coverage has been marked out to be responsible for sustainable photoluminescence efficiency at higher temperature. Enhancement of tunneling rate with increasing InAs SML coverage has been physically described as consequence of reduced average inter-dot lateral separation as estimated from grazing incidence small angle x-ray scattering (GISAXS) measurement. Moreover, we have observed the anomalous decrease of spectral linewidth with temperature which can also be described as a consequence of the tunnel induced faster inter-dot carrier transfer at higher sub-monolayer coverage. The absence of any wetting layer in SML QD resulted in speeding up of carrier transfer through inter-dot tunneling pathways with tunnel time as low as 350 ps. This is significantly faster than the conventional InAs/GaAs SK QDs with tunnel time of 1328 ps.