Current mechanisms in VLWIR Hg1-xCdxTe photodiodes

VLWIR (lambda (c) similar to 15 mum to 17 ym at 78 K) detectors have been c haracterized as a function of temperature to determine the dominant current mechanisms impacting detector performance. I-d - V-d curves indicate that VLWIR detectors are diffusion limited in reverse and near zero bias voltage s down to temperatures in the 40 K range. At 30 K the detectors are limited by tunneling currents in reverse bias. Since the detectors are diffusion l imited near zero bias down to 40 K, the R(o)A(imp) versus temperature data represents the diffusion current performance of the detector as a function of temperature. The detector spectral response measurement and active layer thickness are utilized to calculate the HgCdTe layer x value and the optic al activation energy E-a optical. The activation energy, E-a electrical, Ob tained from the measured diffusion limited R(o)A(imp) versus temperature da ta is not equal to the activation energy, E-a optical, obtained from the sp ectral response measurement for all x values measured. E-a electrical = bet a* E-a optical, where beta ranges between 0.64 and 1.0 For cutoff wavelengt hs in the less than or equal to 9 mum at 78 K, E-a electrical = E-a optical . E-a electrical = 0.65* E-a optical have been measured for lambda (c) = 17 mum at 78 K detectors. As the band gap energy decreases to values in the r ange of 70 meV and lower, it is reasonable to expect a more dominant role o f band tailing effects on the transport properties of the material system. In such a picture, one would expect the optical band gap to be unmodified, whereas the intrinsic concentration could be enhanced from its value for th e ideal semiconductor. Such a picture could explain the observed behavior. Further probing experiments and modeling efforts will help clarify the phys ics of this behavior.