A Highly-Strained InAs/GaSb Type Ⅱ Superlattice for LWIR Detection

摘要

IR photo detectors are in high demand for various military and civilian applications, such as airborne surveillance, remote sensing, environmental monitoring, and spectrometry. Recently InAs/GaSb type Ⅱ superlattice (T2SL) has attracted numerous R&D interest since SLS is the only IR material that has a theoretical prediction of higher performance than HgCdTe. Here we report the improvement of SL photo diodes through a new design with highly-strained type-Ⅱ superlattice (HS-T2SL). The HS-T2SL consists of a highly compressively strained thick InSb layer at InAs/GaSb interfaces. The presence of coherent strain shifts the band edges such that the SL energy gap is reduced. This reduced band gap is advantageous to photodetectors because longer cut-off wavelengths can be obtained with reduced layer thickness in the strained SL. The highly compressive strain in HS-T2SL also leads to an even higher optical absorption coefficient and lower dark current. Applying this new design resistance-area product (R_0A) is measured as high as 2.1 Ohm-cm~2 at 85K for 14.8-μm-cutoff photo diodes without any dark current suppression barriers. The fabricated 14.5μm-cutoff photo diode shows Johnson-noise-limited peak detectivity of 8.4×10~(10) cmHz~(1/2)/W at zero bias at 85K.