The electroreflectance of highly doped semiconductors has been modeled
, taking into account both Franz-Keldysh and band-filling (Moss-Burste
in) effects. Comparisons are made between theoretical and experimental
electrolyte electroreflectance results obtained from an n-type GaAs e
lectrode of dopant density approximately 1 X 10(18) cm-3 in a 0.1-M KO
H solution. The form of the experimental line shape with applied poten
tial is successfully predicted, and details of Fermi-level pinning of
both ac and dc potentials are deduced. Band-gap narrowing and the posi
tion of the Fermi level are discussed and the relative prominence of t
he Franz-Keldysh and Moss-Burstein effects compared, and it is shown t
hat the low mass of the majority carriers implies that the observed li
ne shape can only be accurately modeled when both effects are consider
ed.