Passivation effects on reactive-ion-etch-formed n-on-p junctions in HgCdTe

The formation of n-on-p junctions by reactive ion etching (RIE) of HgCdTe using an H₂/CH₄ plasma has previously been demonstrated to produce high-performance photodiodes. To fully exploit the inherent advantages of this process, a compatible surface-passivation technology that provides long-term stability is required. This paper examines the effects of thermally evaporated CdTe- and ZnS-passivation on RIE-formed photodiodes undergoing low-temperature baking in a vacuum at temperatures typically used for Dewar bakeout. Experimental results show that as a single passivation layer, neither CdTe nor ZnS are suitable for vacuum packaging of RIE-formed diodes that are to be operated at cryogenic temperatures. A double passivation layer, however, consisting of CdTe passivation and an insulating overlayer of ZnS, produces photodiodes that are stable throughout 175 h, approximately 1 week, of 80°C baking in a vacuum.