Interdiffusion Effects on Bandstructure in HgTe-CdTe Superlattices for VLWIR Imaging Applications

In this paper, a systematic study of interdiffusion in (112)B oriented HgTe/CdTe superlattice (SL) structures has been undertaken in order to investigate the viability of employing SL as the absorber layer for very long wavelength infrared (VLWIR, 15 μm and longer) applications in imaging focal plane arrays. Using numerical analysis, the optimal superlattice parameters and annealing time at the growth temperature (∼ 180°C) are found, which result in better control of the cut-off wavelength in superlattice absorbers compared to the corresponding HgCdTe alloy absorber. Simulations show that, by appropriate adjustment of annealing time, it is possible to achieve the same cut-off wavelength with a larger HgTe well width while the sensitivity of the SL to well width variations remains at 15 meV/nm. Furthermore, the electron effective mass in a SL absorber is larger than a HgCdTe alloy absorber, which results in lower tunneling dark current. This work focuses on optimization of the superlattice absorber using the stationary Schrödinger equation. A complete photodetector device design based on a SL absorber structure will require a comprehensive numerical modeling using a Schrödinger–Poisson solver and drift–diffusion solver, or a combination of both approaches, which will be undertaken in the future.