Development of MBE HgCdTe for HDVIP® Focal-Plane Arrays

DRS Technologies is pursuing molecular beam epitaxy (MBE) HgCdTe as an alternative to its standard liquid-phase epitaxy (LPE) double-sided interdiffused (DSID) process for small-pitch, large-area, high-density vertically integrated photodiode (HDVIP ® ) focal-plane arrays (FPAs). Unlike DRS’s Te-rich LPE, which must be thinned from 60 μ m to 5 μ m, MBE material can be grown to the desired thickness. Additionally, the CdTe passivation layers needed for the HDVIP architecture may be grown in situ with MBE, greatly reducing the handling and processing time of DSID material. HDVIP FPAs were fabricated with MBE material that had been passivated with in situ MBE on one surface with CdTe deposited on the other. The MBE FPAs nearly matched the performance of LPE FPAs at 120 K but degraded at 160 K due to noise defects. Dark current measured at 100 K suggested a short lifetime. Additional MBE FPAs were fabricated with a full DSID process after annealing in Hg ambient at either 350°C, 400°C, 425°C or 450°C. The 350°C Hg anneal improved the lifetime of the material, and consequently reduced the number of noise defects at 160 K. Further investigation is warranted to understand how annealing MBE material in Hg ambient impacts HDVIP FPA performance at high temperatures.