The fundamental absorption edge of AlAs and AlP

The fundamental absorption edge of AlAs and AlP was investigated by optical transmission measurements from 2° to 300°K. The absorption edge in both materials is dominated by indirect optical transitions, and values of Eg at 300°K are 2.45 eV for AlP and 2.16 eV for AlAs. The bandgaps at 0° are 2.52 eV and 2.238 eV respectively. The absorption edge structure in AlAs is consistent with the conduction band minima at or near X. It includes impurity-induced bound and free exciton components and phonon-assisted components. The corresponding phonon energies of 13(TA), 27(LA) 42(TO) and 50 meV (LO) have been identified in AlAs. © 1970.