Molecular beam epitaxy grown long wavelength infrared HgCdTe on compliant Si substrates

At the Army Research Laboratory (ARL), a new ternary semiconductor system CdSe_xTe_1-x/Si(211) is being investigated as an alternative substrate to bulk-grown CdZnTe substrates for HgCdTe growth by molecular beam epitaxy. Under optimized conditions, best layers show surface defect density less than 400 cm^-2 and full width at half maximum of X-ray double crystal rocking curve as low as 100 arc-sec with excellent uniformity over 3 inch area. LW-HgCdTe layers on these compliant substrates exhibit comparable electrical properties to those grown on bulk CZT substrates. Photovoltaic devices fabricated on these LWIR material shows diffusion limited performance at 78K indicating high quality material. Measured R_oA at 78K on λ_co = 10 μm material is on the order of 340 Ω-cm₂. In addition to single devices, we have fabricated 256x256 2-D arrays with 40 μm pixel pitch on LW-HgCdTe grown on Si compliant substrates. Data shows excellent QE operability of 99% at 78K under a tactical background flux of 6.7x10¹⁵ ph/cm²sec. Most probable dark current at the peak distribution is 5.5 x 10⁹ e-/sec and is very much consistent with the measured R_oA values from single devices. Initial results indicate NETD of 33 mK for a cut-off wavelength of 10 μm with 40 micron pixels size. This work demonstrates CdSe_xTe_1-x/Si(211) substrates provides a potential road map to more affordable, robust 3^rd generation FPAs.