Spontaneous Emission in TMDs: Exciton Dispersion, Lifetimes and Purcell Factor

Merring-Mikkelsen, Lars ; Sauer, Mikkel Ohm ; Nielsen, Carl Emil Mørch

4. term (FYS10)

Physics, Master

2020

2020-06-03

88

Med udgangspunkt i DFT-beregninger udført i GPAW undersøger vi de excitoniske, optiske og radiative egenskaber i molybdæn- og wolfram-baserede TMD-materialer (transition metal dichalcogenider). Vi løser Bethe-Salpeter-ligningen i en planbølge-basis med et Keldysh-potentiale (en model for, hvordan ladninger vekselvirker i tynde lag). Vi modellerer fladeledningsevnen (sheet conductivity) og absorbansen samt den radiative levetid for lyse (optisk tilladte) excitontilstande, dvs. bundne elektron-hul-par, der kan udsende lys. Levetiderne bestemmes ud fra center-of-mass-impuls-dispersioner i det optiske område, fundet ved først at interpolere tætte DFT-data og derefter iterativt løse BSE. Derudover undersøger vi Purcell-forstærkning af levetiden i en simpel dielektrisk geometri og i et lidt mere komplekst optisk kavitetssystem. Endelig sammenligner vi de modellerede data med PL- og absorptionsmålinger samt anden teori og finder en rimelig overensstemmelse.

Using density functional theory (DFT) with the GPAW code, we examine the excitonic, optical, and radiative properties of molybdenum- and tungsten-based transition metal dichalcogenides (TMDs). We solve the Bethe–Salpeter equation (BSE) in a plane-wave basis with a Keldysh potential (a model for how charges interact in thin layers). We model the sheet conductivity and absorbance, and the radiative lifetime of bright (optically allowed) excitonic states, i.e., bound electron–hole pairs that can emit light. Lifetimes are obtained from center-of-mass momentum dispersions in the optical regime by first interpolating high-density DFT data and then iteratively solving the BSE. We also evaluate Purcell enhancement of the lifetime in a simple dielectric geometry and in a more complex optical cavity. Finally, we compare our modeled results with photoluminescence (PL) and absorption measurements and with other theoretical data, finding reasonable agreement.

[This abstract was generated with the help of AI]

Emission ; TMDs ; Excitons ; BSE ; Bethe-Salpeter ; Purcell ; Purcell Factor ; GPAW ; Lifetimes ; Green's Functions ; DFT ; QFT

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