Electron – Phonon Interaction in Emerging Semiconductors

This thesis is an investigation of the quantized normal mode of vibrations of the constituent atoms of semiconductors, referred to as phonons, and its effect on carrier transport and thermal conductivity of emerging semiconductors. Interaction of charge carriers with phonons is the dominant mechanism through which charge carriers exchange energy with the crystal lattice, hence their proper understanding becomes of prime importance while modelling carrier transport in a semiconductor. The phonon modes undergo significant modification as a result of dimensional confinement or presence of interfaces in semiconductors which must be taken into account while modelling their interaction with charge carriers. The carrier phonon interaction and phonon decay mechanisms are the main topic of study in this thesis applied to the case of emerging semiconductors which are wide band gap and in which electrons couple very strongly to the optical phonons. These emerging semiconductors are finding wide application in high power and high frequency applications. The main findings of this study are: (1) Surface acoustic phonon modelling by quantization of Rayleigh waves on the diamond surface has been done and its interaction with holes present in two dimensional hole gas on the surface has been performed. (2) A novel heterostructure consisting of cubic Boron Nitride and Diamond has been investigated to be used as a High Electron Mobility Transistor. Conditions of production of two dimensional electron gas and its interaction with surface acoustic phonons and remote polar phonon has been studied. (3) Modelling of acoustic phonon decay through three phonon process has been done for wurtzite crystals duly accounting for its anisotropy. Such study is fundamental for evaluation of thermal conductivity of the crystals. (4) Electric field velocity relations and other transport parameters have been evaluated for technologically important wurtzite and emerging cubic crystals under the purview of path integral mechanism (Thornber – Feynman polaron theory). The traditional relaxation time approach based on perturbative techniques breaks down in these materials which warrants use of non-perturbative path integral techniques .Correction factors have been obtained for Fermi’s golden rule to properly account for mobility of charge carriers. (5) Thornber – Feynman’s polaron theory has been extended to emerging two dimensional Transition Metal Di-Chalcogenides. It is demonstrated that Fermi’s golden rule breaks down in these strongly coupled materials. Electric field – velocity relations have been worked out along with carrier mobility. (6) Role of confined optical phonons is investigated in exciton generation for a quantum dot interacting with laser modelled as a classical light. This study forms a basis for qubit state preparation in quantum computing applications.