Studying the physics of excitons in semiconductor quantum heterostructures

Abstract

Semiconductor science and technology has experienced a giant leap in the last few decades due to the invention of sophisticated instruments for efficient growth of semiconductor materials These eventually facilitated the growth of few nanometers thin uniform epitaxial layers and heterostructures with precise control of charge carriers even at such small length scales All these had allowed physicists to explore and manipulate quantum properties of semiconductor structures for both basic physics studies and to realize novel technological applications Excitons are one of the most commonplace and elementary excitations happen in semiconductor systems Contributions of these excitons become even more interesting in quantum heterostructures due to experimental detection of excitonic electro optical effects and large non linear optical effects even at room temperatures Nevertheless past studies of excitons mostly focussed on studying its optical properties However excitons as a composite quasi particle of negatively charged electron and positively charged hole always possess electric dipole moments Thus probing the dielectric polarization of excitons using various opto electrical techniques will be helpful to explore the many body physics of semiconductor heterostructure devices Here in this thesis we mainly aim to probe this inherent dipolar nature of these excitons using voltage and frequency dependent capacitance and photocapacitance measurements in quantum heterostructure devices We would like to mention here that these techniques of sensing dielectric polarization of excitons were not commonly used in the past We also reiterate and explain why some population of excitons in quantum confined heterostructure of III V semiconductors can survive at high enough temperatures such that thermal energy kBT is more than the binding energy of excitons This is in contrast to widespread misunderstandings of treating excitons as mostly low temperature objects We also demonstrate that voltage activated rate processe newline