Growth of InAs/Ga 1−xIn xSb infrared superlattices

Abstract

A set of InAs/Ga 1−xIn xSb superlattices has been grown by molecular beam epitaxy. The superlattices are deposited on thick, stress-relaxed buffer layers of GaSb on (100)-oriented GaAs substrates. A short-period, heavily strained superlattice has been inserted at the GaAs/GaSb interface. Transmission electron microscope (TEM) images reveal that a dense network of dislocations forms at this interface, with the vast majority of threading dislocations propagating no further than the first 1000 Å of the GaSb buffer layer. Planar superlattice layers are observed, with ni evidence of stress relaxation between the layers or between the InAs/Ga 1- x In xSb superlattice and GaSb buffer. Analysis of X-ray diffraction satellites reveals that cross-incorporation of As in GaSb and Ga 1−xIn xSb layers is virtually eliminated at low growth temperatures. Photoconductivity spectra from the superlattices display sharp photocurrent threshold energies, in agreement with previously published energy gaps derived from calculations and photoluminescence data. Thresholds in the 8–14 μm range are obtained from superlattices with very thin layers ( ≈ 40 Å), which are necessary for strong optical absorption in a type II superlattice. Finally, an absorption coefficient of ≈ 2000 cm −1 is measured at 10 μm from a superlattice with an energy gap of 11.4 μm. This value is comparable to that of bulk Hg 1−xCd xTe, the current industry standard for infrared detectors in the 8–14 μm range.