Comment on `Modelling the optical constants of GaAs:excitonic effects at E1,E1 + Δ1 criticalpoints'

Abstract

Djurisic and Li (1999, Semiconductor Science andTechnology 14 958) have recently presented acalculation of the optical constants of GaAs in which they donot take into account excitonic effects at either E1,E1 + Δ1 or E0,E0 + Δ0 critical points (CPs).They employ band-to-band single-particle expressions withan energy-dependent pseudo-Gaussian broadening function.Their paper states that including excitonic effects at theformer CPs has `dubious physical interpretation'. It is alsoclaimed that (a) `excitonic effects are usually more pronouncedat E0,E0 + Δ0 than at the E1,E1 + Δ1 CPs',(b) `at room temperature the excitons are severelybroadened and should not contributesignificantly to the dielectric function' and (c) `excitoniceffects at E1,E1 + Δ1 critical points do not represent asignificant contribution to the dielectric function at roomtemperature for materials with low exciton binding energy'.These statements are completely incorrect, as is their fittingscheme.