Interface optimization and fabrication of InAs/GaSb type II superlattice for very long wavelength infrared photodetectors

We developed a new strategy for the optimization of InSb interface properties of very long wavelength infrared InAs/GaSb superlattice. The superlattice structures with different InSb interface thickness were fabricated to optimize the strain balanced between the superlattice and GaSb substrate. The SL structure containing 16 ML InAs/7 ML GaSb with the InSb interface layer thickness of 0.9 ML in each period shows the smallest stain of +0.065% and full width half maximum (FWHM) of the 1st order peaks of 24 arcsec. We also demonstrated the InAs/GaSb photodiodes with PIN structure operating at 77 K. The photodiodes have a 50% cutoff wavelength of 14.4 μm. The peak responsivity of the devices at zero bias is about 0.54 A/W at12.1 μm leading to the external quantum efficiency of 5.5%. With the R₀A of 0.126 Ωcm², the device has a Johnson noise limited D∗of 2.94 × 10⁹ cmHz^1/2W^-1 at 77 K under zero bias.