The influence of dislocations on the electrical and photo-electric characteristics of HgCdTe has been widely discussed in
published literature. However, an unexplored aspect of the dislocations that has not yet attracted the attention of any of
the investigators, is the band gap narrowing/widening induced by the intense stress field around dislocation core.
Preliminary estimations show that the band gap narrowing due to the tensile region of the stress field along the
dislocations in HgCdTe is high enough to cause significant band gap narrowing in low band gap HgCdTe. An enhanced
Zener like band-to-band tunneling is proposed in the vicinity of dislocation cores. The calculations presented here
qualitatively explain the observed influence of dislocations on HgCdTe photodiode characteristics.
This paper reports the possibility of assessing the relative surface and bulk contributions in HgCdTe junction diodes by analyzing the Current - voltage (I - V) and dynamic impedance - voltage (R<sub>d</sub> - V) characteristics of an individual diode. As an example, an analysis of the experimental data obtained on diodes fabricated in our laboratory on bulk grown p-type HgCdTe wafers using B<sup>+</sup> implantation and ZnS passivating layers will be presented.
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 H<SUB>2</SUB> 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 Hg<SUB>1-x</SUB>Cd<SUB>x</SUB>Te 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.