TY - BOOK

T1 - Ab initio modelling of two-dimensional semiconductors

AU - Hunt, Ryan James

PY - 2019

Y1 - 2019

N2 - We study excited-state phenomena in a variety of semiconductor systems, withuse of the variational and diffusion quantum Monte Carlo (QMC) methods.Firstly, we consider the formation of charge-carrier complexes in theMott-Wannier model, for systems of restricted geometrical freedom (the coupledquantum well bilayer, and the quantum ring). We find in such systems thatgeometrical constraints lead to the characteristic formation of certaincharge-carrier complexes, and highlight how such effects are of relevance tothe interpretation of recent experiments.Secondly, we illuminate a key difference between two-dimensional systems formedfrom geometrical restriction, and those which are truly two-dimensional inextent, by introduction of the Keldysh interaction. We then studythe formation of charge-carrier complexes in two-dimensional semiconductors andtheir heterostructures in the so-called Mott-Wannier-Keldysh model, derivingappropriate extensions of the Keldysh interaction as necessary.Thirdly, we undertake a comprehensive survey of the use of continuum QMCmethods to evaluate excited-state properties in a truly ab initiofashion, establishing best-practices, and presenting energy gap calculationsfor several real materials. This includes the first published QMC calculationof the electronic energy gaps of a two-dimensional semiconductor, phosphorene.Finally, we propose an extension of the Keldysh interaction which permits thestudy of continuum phases, the so-called ``periodic Keldysh interaction'', anduse it to probe the possible Wigner crystallisation of electrons in aweakly-doped two-dimensional semiconductor.

AB - We study excited-state phenomena in a variety of semiconductor systems, withuse of the variational and diffusion quantum Monte Carlo (QMC) methods.Firstly, we consider the formation of charge-carrier complexes in theMott-Wannier model, for systems of restricted geometrical freedom (the coupledquantum well bilayer, and the quantum ring). We find in such systems thatgeometrical constraints lead to the characteristic formation of certaincharge-carrier complexes, and highlight how such effects are of relevance tothe interpretation of recent experiments.Secondly, we illuminate a key difference between two-dimensional systems formedfrom geometrical restriction, and those which are truly two-dimensional inextent, by introduction of the Keldysh interaction. We then studythe formation of charge-carrier complexes in two-dimensional semiconductors andtheir heterostructures in the so-called Mott-Wannier-Keldysh model, derivingappropriate extensions of the Keldysh interaction as necessary.Thirdly, we undertake a comprehensive survey of the use of continuum QMCmethods to evaluate excited-state properties in a truly ab initiofashion, establishing best-practices, and presenting energy gap calculationsfor several real materials. This includes the first published QMC calculationof the electronic energy gaps of a two-dimensional semiconductor, phosphorene.Finally, we propose an extension of the Keldysh interaction which permits thestudy of continuum phases, the so-called ``periodic Keldysh interaction'', anduse it to probe the possible Wigner crystallisation of electrons in aweakly-doped two-dimensional semiconductor.

KW - Two-dimensional (2D) crystals

KW - quantum Monte Carlo

KW - First-principles calculations

KW - excited states

KW - energy gap

U2 - 10.17635/lancaster/thesis/769

DO - 10.17635/lancaster/thesis/769

M3 - Doctoral Thesis

PB - Lancaster University

ER -