Type-II InAs/GaSb superlattices grown by molecular beam epitaxy for infrared detector applications

Two type-II superlattice structures with 15 monolayer (ML) InAs/12ML GaSb and 17ML InAs/7ML GaSb grown on GaSb (100) substrates by solid-source molecular beam epitaxy (MBE) have been investigated. The X-ray diffraction (XRD) measurements of both the 15ML InAs/12ML GaSb and 17MLInAs/7ML GaSb superlattices indicated excellent material and interface qualities and very narrow full width at half maximum (FWHM) of the zeroth-order peaks which were 22 arcsec and 20 arcsec respectively. The cutoff wavelengths of 15ML InAs/12ML GaSb and 17ML InAs/7ML GaSb superlattices photodetectors were measured at 6.6 mu m and 10.2 mu m, respectively. These different spectral ranges were achieved by growing alternating layers of variable thicknesses and in addition, the band gap engineering offered by the superlattices of InAs and GaSb. A zero-bias Johnson-noise-limited detectivity of 1.2x10(11) cmHz(1/2)/W at temperature 80K and wavelength of 6 mu m was achieved for an unpassivated photodiode of 15ML InAs/12ML GaSb superlattice, and the detectivity at 80K and 9 m was 2.2x10(10) cmHz(1/2)/W for the device of 17ML InAs/7ML GaSb superlattice. Also, the optical and electrical characteristics of 15ML InAs/12ML GaSb superlattice photodiode were investigated from 80K to 280K. A zero-bias Johnson-noise-limited detectivity at temperature of 210K and wavelength of 6 mu m was 1.2x10(8) cmHz(1/2)/W.