Two-photon absorption spectrum of AlAs-GaAs monolayer crystals

The excitation spectrum of two-photon absorption of 1.1±0.1:9.4±0.6 AlAS: GaAs monolayer crystals was measured by the luminescence technique. The observed transitions to the $n=1\mathrm{}$ exciton are attributed to the three-band model. The 5.3-meV splitting of the exciton is primarily due to the splitting of the two hole bands by the periodic potential, which is also responsible for an upward shift of the band gap relative to a random alloy having the same average composition. The band to band two-photon absorption spectrum has the characteristics of the two-band model previously found for GaAs. The two-photon absorption spectrum thus indicates that while the band structure of the monolayer crystal has certain similarities to the band structures of bulk GaAs and the random alloy, the details may be significantly different.