Electrical and optical investigations of the condensed matter physics of junction diodes under charge carrier injection

Abstract

In this thesis we present our studies of the dielectric properties of junction baseddiode structures under charge carrier injection This regime remains less explored evenafter decades of research in the field of semiconductors However it is a necessaryworking condition for a set of diodes like electroluminescent diodes producing lightemission and hence important from the fundamental and application points of view Nevertheless the presence of a large number of free charge carriers in this regime givingrise to different time scale processes and possibility of carrier interactions imposesexperimental challenges and complexities In such a scenario conventionalcharacterization techniques and understanding of junction diodes based on depletionapproximation and electrostatics break down Hence we modified the existing techniquesand developed new techniques and analyses to probe electroluminescent diode structuresunder charge injection We observed counter intuitive response beyond the availableunderstanding of these structures We probed the connection between electrical andoptical properties and its manifestations to understand carrier transport in these activedevices We used impedance spectroscopy and developed voltage modulatedelectroluminescence spectroscopy to study mainly AlGaInP based multi quantum wellelectroluminescent diodes ELDs for relatively low frequencies We observed that underhigh injection reactance of the diodes acquires inductive like behavior which isperceived as negative capacitance NC Occurrence of NC was found to be accompaniedby the onset of modulated light emission Magnitudes of both increase in a correlatedfashion with decreasing modulation frequencies These observations are technologicallyimportant but are beyond the conventional diffusion capacitance model of the diodeunder forward bias We explained that this interdependence of electric newline newline