Optical Absorption Due to Excitation of Electrons Bound to Si and S in GaP

Abstract

Infrared transmission measurements of GaP with S or Si donor impurities at liquid-helium temperature reveal absorption lines due to excitation of the donor electron. Strong absorption peaks corresponding to the $1s\ensuremath{\rightarrow}2{p}_{\ifmmode\pm\else\textpm\fi{}}$ transition are observed, and their spectral positions are used to determine optical ionization energies of 104.2 and 82.5 meV (\ifmmode\pm\else\textpm\fi{}0.3 meV), respectively, for S and Si donors in GaP. A fitting of Faulkner's effective-mass calculation for donor states to the observed levels yields the effective masses of the conduction band: ${m}_{\ensuremath{\perp}}=(0.191\ifmmode\pm\else\textpm\fi{}0.005){m}_{0}$ and ${m}_{\mathrm{II}}=(1.7\ifmmode\pm\else\textpm\fi{}0.2){m}_{0}$. The $p$-like final states observed in these measurements are found to differ significantly in binding energy from the excited donor-electron states observed in the two-electron recombination of the exciton bound to neutral sulfur in GaP.