NASA NTRS1990
The successful growth of InAs/Ga(1-x)In(x)Sb superlattices and their optical and structural characterization is discussed. Samples were grown by molecular beam epitaxy at fairly low substrate temperatures (less than 400 C). Structural quality was assessed by reflection high energy electron difrraction, transmission electron microscopy, and x ray diffraction. Excellent structures were achieved for growth on thick, strain relaxed GaSb buffer layers on GaAs substrates, despite a residual threading dislocation density of 10(exp 9)cm(exp -2) originating at the GaSb/GaAs interface. Despite a lattice mismatch of 1.7 percent, InAs/Ga(0.75)In(0.25)Sb superlattices are observed to be free of misfit dislocations at the thicknesses examined here, owing to the close lattice match between the superlattice and GaSb, which evenly distributes compressive and tensile stresses between the InAs and Ga(0.75)In(0.25)Sb layers. Photoluminescence and photoconductivity measurements indicate that the energy gaps of the strain-layer superlattices are smaller than those of InAs/GaSb superlattices with the same layer thicknesses, and are in agreement with the theoretical predictions of Smith and Mailhiot. Energy gaps of 80 to 250 meV (15 to 5 microns) have been measured for InAs/Ga(0.75)In(0.25)Sb superlattices with 45 to 25 A/25 A layer thickness. Results demonstrate that far-infrared cutoff wavelengths are compatible with the thin superlattice layers required for strong optical absorption in type-II superlattices.