InAs/GaSb type-II superlattices for high performance mid-infrared detectors

The superlattice (SL) design parameters of a 50 period InAs/GaSb SL structure with InSb-like interfaces (IFs) were systematically varied around the 26Å InAs/27Å GaSb design in order to explore the parameter space for maximum photoresponse in the 3-5μm mid-infrared atmospheric window. Using previously optimized growth conditions, the SL structures were grown on p-type GaSb substrates by molecular beam epitaxy with precisely calibrated growth rates. The electrical properties of the SLs were characterized by magnetic field-dependent Hall effect measurements below the carrier freeze-out temperature of the p-type substrate. Multi-carrier analysis at 4.2 K determined an electron sheet carrier concentration of 8.5×1010cm-2 with a mobility of 8200cm2/Vs. Two sets of SLs were used in the optimization process: the first set with a fixed InAs width of 26 Å, and the second with a fixed GaSb width of 27Å. As the GaSb layer width varied from 15 to 27Å, the photoresponse cut-off wavelength shifted from 6.47 to 5.24μm. Similarly, as the InAs width varied from 26 to 13 Å, the cut-off wavelength shifted from 5.08 to 3.05μm. The strongest photoresponse in the 3-5μm mid-IR window was achieved with the InAs (20 Å)/GaSb (27 Å) SL design.