Electrical properties of epitaxially grown CdTe passivation for long-wavelength HgCdTe photodiodes

Results of experimental measurements and theoretical analysis are presented for the TiAu/ZnS/CdTe/HgCdTe metal–insulator–semiconductor heterostructure. The passivation of HgCdTe is provided by a double layer consisting of a dielectric ZnS placed on top of an epitaxial CdTe layer. Both HgCdTe and CdTe were grown by metalorganic chemical vapor deposition. Two types of CdTe layers were investigated: one was grown directly, in situ, immediately following the growth of HgCdTe; the second was grown indirectly using previously grown HgCdTe samples. It is shown that directly grown CdTe layers lead to low fixed interface charge, which is a good condition for passivation. The indirectly grown samples are still acceptable, but not as good as the directly grown samples. We demonstrate, on the basis of theoretical considerations, that the dielectric ZnS improves the flatband condition at the CdTe/HgCdTe interface.