Optical properties of ultrathin 50nm GaAs membranes

Ultra thin films of single crystal GaAs have been fabricated by selective etching of epitaxial layers grown by Molecular Beam Epitaxy. The resulting membranes are 50nm thick. The results of optical absorption and photoconductivity (PC) measurements are presented. The results demonstrate features which are not normally observed in thicker GaAs layers. The optical absorption shows a large absorption below the fundamental band edge due to the Franz-Keldysh effect. Higher energy transitions from the valence to conduction band at the L point in the Brillouin zone are also observed in the optical absorption spectra of these structures, this occurs at 2.7 eV. The temperature dependence of this energy gap is measured and compared with previous data. The PC spectra show oscillations above the band edge, the origin of this is uncertain. © 1995.