Reflectance of AlAs-GaAs and In0.28Ga0.72As-GaAs superlattices

Abstract
Reflectance measurements are reported for In0.28Ga0.72As‐GaAs and AlAs‐GaAs superlattices over the wavelength range 300–500 nm. Superlattice layer thicknesses ranged from 46 to 368 Å for the In0.28Ga0.72As‐GaAs film samples and from 77 to 612 Å for the AlAs‐GaAs specimens. Peaks corresponding to the E1 and E11 transitions of GaAs are present in all of the AlAs‐GaAs spectra. Size quantization is found to have little effect on the energy positions of these peaks because of the large effective mass and parallel curvature of the conduction band near the L valleys in this semiconductor. The AlAs E1 transition, observed previously in electroreflectance studies, also appears in the AlAs‐GaAs superlattice reflectance and increases in energy as the superlattice layer thickness decreases. The In0.28Ga0.72As‐GaAs reflectance spectra for superlattice layer thicknesses less than 150 Å contain peaks similar to the E1 and E11 transitions for In0.28Ga0.72As and GaAs. The lower energy peak occurs around 2.8 eV, which is intermediate between the E1 transitions for In0.28Ga0.72As (2.67 eV) and GaAs (2.92 eV). Similarly, the higher energy peak at 3.03 eV falls between the E11 peaks for In0.28Ga0.72As (2.90 eV) and GaAs (3.14 eV). For superlattice layer thicknesses greater than 150 Å, a third peak appears near the In0.28Ga0.72As E11 transition.