Microscopic Theory of Linear and Nonlinear Optical Response: zinc-blende semiconductors
Translated title
Microscopic Theory of Linear & Nonlinear Optical Response
Author
Trolle, Mads
Term
4. term
Education
Publication year
2011
Pages
116
Abstract
Afhandlingen undersøger, hvordan mikroskopiske, båndstrukturbaserede modeller kan forudsige teknologisk relevante lineære og ikke-lineære optiske egenskaber i zinc-blende halvledere (GaAs, InSb, Ge og Si). Den empiriske pseudopotentialmetode, både med og uden spin-banekobling, kombineres med lineær-analytisk tetrahedronintegration over Brillouin-zonen for at beregne frekvensafhængig lineær susceptibilitet, herunder effekter af rumlig dispersion ved at inddrage fotonens bølgevektor. Bulk andenharmonisk generation behandles i dipoltilnærmelsen for GaAs og InSb, og konsekvenserne af rumlig dispersion for andenharmoniskresponsen i Ge og Si analyseres. Elektrisk-felt-induceret andenharmonisk generation fra overfladeudtømningslag modelleres, og de tilsvarende tensorelementer estimeres for alle fire materialer. For at adressere overflader og tyndfilm tilpasses metoden til ideelle to-dimensionelle tyndfilm (uden rekonstruktion), hvilket muliggør beregning af overfladebåndstrukturer, tilstandstæthed samt in-plane og out-of-plane lineære spektre; en fremgangsmåde til beregning af overflade-SHG præsenteres og anvendes på Ge. På makroskopisk niveau gennemgås modeller for et semiuendeligt medium med en overflade og for plader af endelig tykkelse, som forbinder den mikroskopiske andenordens susceptibilitet med målbare SHG-signaler. Endelig beskrives SHG-eksperimenter på en GaAs-wafer og diskuteres i forhold til de beregnede spektre og til tidligere resultater, der inkluderer eksitoniske effekter.
This thesis examines how microscopic, band-structure-based models can predict technologically relevant linear and nonlinear optical properties of zinc-blende semiconductors (GaAs, InSb, Ge, and Si). The empirical pseudopotential method, with and without spin–orbit coupling, is combined with the linear-analytic tetrahedron integration over the Brillouin zone to compute frequency-dependent linear susceptibility, including spatial dispersion by incorporating the photon wave vector. Bulk second-harmonic generation is treated in the electric-dipole approximation for GaAs and InSb, and the impact of spatial dispersion on the second-harmonic response of Ge and Si is analyzed. Electric-field-induced second-harmonic generation from surface depletion layers is modeled, and the corresponding tensor elements are estimated for all four materials. To address surfaces and thin films, the method is adapted to ideal two-dimensional thin films (neglecting reconstruction), enabling calculations of surface band structures, densities of states, and in-plane/out-of-plane linear spectra; a procedure for computing surface SHG is presented and applied to Ge. At the macroscopic level, models for a semi-infinite medium with a surface and for finite-thickness slabs are reviewed, linking microscopic second-order susceptibility to measurable SHG signals. Finally, SHG experiments on a GaAs wafer are described and discussed in relation to the calculated spectra and prior results that include excitonic effects.
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