Optical absorption of radio frequency sputtered GaAs(Ti) films

Abstract

Composition and optical absorption of thin films of GaAs(Ti) and GaAs, deposited by sputtering on glass substrates under different process conditions, have been investigated. The thin films obtained are typically 200 nm thick. ToF–SIMS measurements show a quite constant concentration and good uniformity of Ti profiles along the GaAs(Ti) layers in all cases and EPMA results indicate that Ti content increases with the substrate temperature in the sputtering process. Measurements of the transmittance and reflectance spectra of the GaAs and GaAs(Ti) thin films have been carried out. In the optical characterization of the films it is found that optical absorption is enhanced in all samples containing Ti. The determination of the optical gap from the optical absorption, shows optical gap variations from 1.15 to 1.29 eV in the GaAs thin films, and from 0.83 to 1.13 eV in the GaAs(Ti) thin films. The differences in absorption and EgTAUC observed between samples of GaAs and GaAs(Ti) are consistent with the presence of an intermediate band.