Study of carrier lifetime degradation in (Zn)CdTe/MgCdTe double heterostructures

(Zn)CdTe/MgCdTe double heterostructures (DH) are grown on InSb substrates using MBE. The DHs are capped with 10~30 nm (Zn)CdTe layers to prevent MgCdTe from oxidization. The carrier lifetimes of the DHs with Mg0.24Cd0.76Te barrier layer degrade fast within the first week in atmosphere and then at a much slower rate. The carrier lifetime degradation is about 20-30% compared with the initial value. However, for the DHs with Mg0.36Cd0.64Te barrier layer, the carrier lifetime is stable over time. The degradation of the lifetime for samples with Mg0.24Cd0.76Te barrier is attributed to the degradation at the surface of (Zn)CdTe cap, since photogenerated carries can more easily overcome the lower Mg0.24Cd0.76Te barrier layer through thermionic emission and recombine non-radiatively at the top surface. The Mg0.36Cd0.64Te barrier with a much higher potential height will prevent those carriers from escaping the CdTe region, thus resulting in a much longer carrier lifetime and less impact from surface conditions.