Use this URL to cite or link to this record in EThOS:
Title: The metal-insulator transition in doped semiconductors : an ab initio approach
Author: Carnio, Edoardo
ISNI:       0000 0004 7425 648X
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2018
Availability of Full Text:
Access from EThOS:
Access from Institution:
In this thesis we study the Anderson metal-insulator transition starting from an atomistically correct ab initio description of a doped semiconductor. In particular, we use density functional theory to simulate model systems of sulphur-doped silicon (Si:S) with few impurities in a large cell. From the resulting Kohn-Sham Hamiltonian, we build an effective tight-binding Hamiltonian for larger systems with an arbitrary number of dopants. Our effective model assumes the same potential around single and paired impurities, for up to ten nearest neighbours and disregarding configurations of three and more close impurities. We generate up to a thousand disorder realisations for systems of 16 3 to 22 3 atoms and a large range of impurity concentrations. From the diagonalisation of these realisations we study the formation of an impurity band in the band gap of the host semiconductor. With increasing impurity concentration, this band undergoes an Anderson metal-insulator transition, namely (i) it approaches and merges with the conduction band and (ii) its states delocalise starting from the band centre. From the multifractal fluctuations of the wave functions near criticality, we characterise the Anderson transition in terms of its critical concentration nc and exponent. We identify two regimes: for energies in a “hybridization region”, where the conduction band seems to influence the impurity band, we observe an increase from v ≈ 0:5 to v ≈ 1, compatibly with the experimental values; deeper in the band, instead, the estimates of v fluctuate between 1 and 1:5, compatibly with v ≈ 1:59 (v ≈1:3) found in the Anderson model without (with) electron-electron interactions. Our results suggest a possible resolution of the long-standing exponent puzzle due to the interplay between conduction and impurity states.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics