Surface leakage current mechanisms in HgCdTe gate controlled photodiodes

HgCdTe gated photodiodes are studied theoretically and experimentally for surface leakage current mechanisms limiting diode performance. Use of a second field plate beyond the perimeter gate has allowed clear identification of leakage components associated with surface state generation, depletion region generation, and field induced tunneling. The fundamental features of the leakage current profiles are derived from MOS theory, and exhibit characteristics similar to the properties of the SiO2/Si interface with some added features peculiar to narrow bandgap semiconductors. Both boron implanted and double layer p-n junction devices in the 2 to 5 µm range are examined. Surface potential was found to have a significant effect on diode impedance and breakdown characteristics. Minimum surface state densities derived from diode leakage current versus gate bias curves were in the range of 10¹¹cm^-2eV^-1.