Time resolved oscillation of excitonic light emission using voltage pulse

Abstract

Understanding the charge transport and characterisation of noise of a low-dimensional semiconductor is a primary step towards the development of stable optoelectronic devices. A study of semiconductor heterostructures previously revealed many novel quantum-mechanical phenomena, which were later translated into new technologies. The Coulomb interaction between electrons and holes gives rise to a bound state known as an exciton. The energy levels of an exciton are very similar to those of a hydrogen atom. This thesis investigates the photoconductance and its standard deviation of a single-crystal, quantum-dot-quantum-well heterostructure of III-V materials, which exhibits excitonic behaviour at cryogenic temperatures. The collective dynamics of excitons are observed in many physical, chemical and biological systems. To probe them, measurements were conducted over a wide range of temperatures, AC modulation frequencies, AC RMS voltages, and light intensities. The measurements revealed that not only does the photoconductance oscillate with applied bias voltage due to coherent resonant tunnelling, but also that the standard deviation exhibits a periodic pattern with applied bias voltage. And these are not merely some experimental artefact but a property of the sample under investigation. Increasing the temperature dampened the oscillation amplitude and standard deviation of photoconductance, with the oscillation vanishing at 175K and 100K, respectively. Another crucial observation is made that the period of the Johnson noise closely matches with the standard deviation providing a crucial insight that the oscillation of the variancce may be closely related to the thermal noise.