Modeling the Optical Constants of Diamond- and Zincblende-Type Semiconductors: Discrete and Continuum Exciton Effects at E0 and E1

Abstract

We present a comprehensive model dielectric function ε(E) [= ε1 + iε2] for diamond- and zincblende-type semiconductors based on the energy-band structure near critical points (CPs) plus discrete as well as continuum excitonic effects at the E0, E0 + Δ0,, E1, and E1 + Δ1 CPs. In addition to the energies of these band-to-band CPs, our analysis also yields information about the binding energies of not only the 3D exciton associated with E0 (R0), when resolved, but also the 2D exciton related to the E1, E1 + Δ1 CPs (R1). This model has been applied to spectral ellipsometry measurements of ε1, ε2 (0.3 eV < E < 5.5 eV) of ZnCdSe/InP, CdTe1—xSx, In0.66Ga0.34As, and GaSb and a surface photovoltage spectroscopy determination of the absorption coefficient of GaAs near E0. This work shows conclusively that even if the exciton at E0 is not resolved the lineshape is continuum exciton. The obtained values of R1 exhibit a trend which is in good agreement with effective mass/k · p theory. Our analysis will be compared with the modeling of Adachi and the University of Illinois-Chicago group, both of whom neglect exciton continuum effects and hence have not evaluated R1. Our results, particularly for exciton continuum effects at E1, have considerable implications for recent first-principles band structure calculations which include exciton effects.