Study of opto electrical properties of excitonic heterostructures and measurement of spatio temporal coherence using a single interferometer

Abstract

This thesis presents opto electrical studies of III V based quantum heterostructures to understand the underlying many body physics of excitons or electron hole pairs With the progress of advanced fabrication techniques over the years high quality samples with cleaner interfaces are realized That provides greater control over the dynamics of these excitons and offers an opportunity to explore the fundamental physics and utilize these for various applications Experimental investigations of quantum correlations of optical and electrical properties of these excitons can also be intriguing In this thesis we also developed a modified optical interferometer that can measure such quantum correlations of excitons through optical emissions First we probed an III V quantum dot QD quantum well QW heterostructure based light emitting p i n diode using electroluminescence measurements under a wide range of carrier injections and at different temperatures The initial lower current bias at 8 Kelvin shows luminescence originates only from the QW even in the presence of QDs having lower energy levels However above some threshold levels of carrier injections light emissions from QDs start Further increase in current contributes to the exponential increase in QD emission while QW emission remains saturated This behaviour points toward a potential barrier between QW and QD which we argue can form by diffusion of the electrons from the conduction band of QW to the conduction band of QDs due to their energy difference With the help of the study of electroluminescence vs bias current and voltage we approximated an empirical formula that quantified the role of this barrier in QD emission Furthermore we separately analysed the emission from QD and QW for temporal coherence with respect to bias current and temperature The observed decline in optical coherence of QDs with increasing bias is attributed to the non radiative Auger recombination process while the same reason explains the unanticipated increase of optical coherence