Author: ALAN BERNAL

AB-INITIO CALCULATION OF TWO-PHOTON ABSORPTION FOR SEMICONDUCTORS

ALAN BERNAL (2022)

"A theoretical derivation of two-photon absorption (2PA) from bulk, surface and 2 dimensional (2D) semiconductors, based on the length gauge analysis and the electron density operator, is formulated; the intraband r_i part and the interband r_e part of the position operator r are properly accounted for. Within the independent particle approximation, the nonlinear third order susceptibility tensor χ abcd (−ω; −ω, −ω, ω) and the two-photon absorption coefficient are calculated, including the scissors correction needed to correct the well-known underestimation of the local-density-approximation band gap. Using time-reversal symmetry, it is shown that the expression for χ abcd (−ω; −ω, −ω, ω) is finite at ω = 0, avoiding nonphysical divergences presented in previous calculations when ω → 0. Ab initio band structure calculations using different pseudopotential schemes that include spin-orbit coupling are used to calculate the 2PA for several semiconductors, and the calculations are compared with available experimental results for photon energies that are below the optical band gap."

Doctoral thesis

Two-photon Absorption Semiconductors CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA ÓPTICA