RIE-induced n-on-p junction HgCdTe photodiodes: effects of passivant technology on bake stability

Reactive ion etching (RIE) of HgCdTe using CH4:H2 is known to generate p- to n-type conversion in both intrinsically doped and extrinsically doped p-type HgCdTe. The use of RIE to form n-on-p junctions in planar diodes has a number of advantages including state of the art diode performance, high uniformity, passivation of the junction at the surface throughout processing, the possibility of the formation of deep junctions, and removal of any need for high temperature processing after junction formation. However, it has long been believed that H2 based plasma junction formation techniques will be long-term unstable. Initial results are presented indicating that surface passivation plays a major role in determining the stability of planar junctions formed using H2 based RIE. Comparisons of ZnS and CdTe passivation for n-on p-junctions formed on x approximately 0.3 Hg1-xCdxTe show dramatic differences in 2 to 3 hour, 80 degrees C bake stability tests. Diodes fabricated using either passivant initially exhibit R0A performance close to the theoretical limit, but are degraded after a 2 hour, 80 degrees C bake. Diodes with CdTe passivation have moderate performance as fabricated, but exhibit improvement rather than degradation after 3 hour, 80 degrees C bake. Such results indicate that planar junctions formed using H2 based RIE may offer a viable technology for low cost, highly uniform, large area IR detector arrays if passivation issues are satisfactorily resolved. Finally, a dual layer ZnS/CdTe passivation process is introduced which results in bake-stable devices after a 17 hour, 80 degrees C bake.