A CdTe passivation process for long wavelength infrared HgCdTe photo-detectors

Passivant-Hg_1−xCd_xTe interface has been studied for the CdTe and anodic oxide (AO) passivants. The former passivation process yields five times lower surface recombination velocity than the latter process. Temperature dependence of surface recombination velocity of the CdTe/n-HgCdTe and AO/n-HgCdTe interface is analyzed. Activation energy of the surface traps for CdTe and AO-passivated wafers are estimated to be in the range of 7–10 meV. These levels are understood to be arising from Hg vacancies at the HgCdTe surface. Fixed charge density for CdTe/n-HgCdTe interface measured by CV technique is 5×10¹⁰ cm⁻², which is comparable to the epitaxially grown CdTe films. An order of magnitude improvement in responsivity and a factor of 4 increase in specific detectivity (D*) is achieved by CdTe passivation over AO passivation. This study has been conducted on photoconductive detectors to qualify the CdTe passivation process, with an ultimate aim to use it for the passivation of p-on-n and n-on-p HgCdTe photodiodes.