Modeling the optical constants of diamond- and zincblende-type semiconductors: Discrete and continuum exciton effects at E-0 and E-1

We present a comprehensive model dielectric function epsilon(E) [= epsilon( 1) + i epsilon(2)] 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 E-0, E-0 + Delta(0), E-1, and E-1 Delta(1) CPs. In addition to the energies of these band-to-band CPs, our an alysis also yields information about the binding energies of not only the 3 D exciton associated with E-0 (R-0), when resolved, but also the 2D exciton related to the E-1, E-1 + Delta(1) CPs (R-1). This model has been applied to spectral ellipsometry measurements of epsilon(1), epsilon(2) (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 G aAs near E-0. This work shows conclusively that even if the exciton at E-0 is not resolved the lineshape is continuum exciton. The obtained values of R-1 exhibit a trend which is in good agreement with effective mass/k . p th eory. Our analysis will be compared with the modeling of Adachi and the Uni versity of Illinois-Chicago group, both of whom neglect exciton continuum e ffects and hence have not evaluated R-1. Our results, particularly for exci ton continuum effects at E-1, have considerable implications for recent fir st-principles band structure calculations which include exciton effects.