Hole effective masses and subband splitting in type II superlattice infrared detectors
We explore band structure effects to help determine the suitability of n type type II superlattice (T2SL) absorbers for infrared detectors. It is often assumed that the exceedingly large growth direction band edge curvature hole effective mass in n type long wavelength infrared (LWIR) T2SL would lead to low hole mobility and therefore low detector collection quantum efficiency. We computed the thermally averaged conductivity effective mass and show that the LWIR T2SL hole conductivity effective mass along the growth direction can be orders of magnitude smaller than the corresponding band edge effective mass. LWIR InAs/GaSb T2SL can have significantly smaller growth direction hole conductivity effective mass than its InAs/InAsSb counterpart. For the InAs/InAsSb T2SL, higher Sb fraction is more favorable for hole transport. Achieving long hole diffusion length becomes progressively more difficult for the InAs/InAsSb T2SL as the cutoff wavelength increases, since its growth direction hole conductivity effect.