Properties of metal-organic chemical-vapor-deposition mercury telluride contacts on p-type cadmium telluride

Abstract

The semimetal‐semiconductor HgTe/CdTe (p‐type) graded heterostructures were formed by the epitaxial growth of HgTe on 〈111〉‐oriented CdTe substrates using metal‐organic chemical‐vapor‐deposition. These graded heterostructures are lattice matched, have a high degree of structural perfection, and the semimetallic HgTe provides both the high electron affinity and high carrier concentration required for ohmic contacts. Unlike the abrupt HgTe/CdTe heterostructure which is rectifying due to the valence‐band offset and interface charges that reside on the polar surfaces of 〈111〉‐oriented CdTe, the graded heterostructures form ohmic contacts. The contact specific resistance can be as low as 0.4 Ω cm² and is determined by the transmission line method on HgTe/Ti/Au stripes processed by ion‐beam milling (on CdTe bulk with resistivity of 10 Ω cm). The contacts are characterized electrically by current‐voltage and dynamic resistance‐voltage characteristics. Auger depth profile and morphology of contacts grown on the A and B faces are compared. Double‐crystal rocking curves characterize the structural perfection of the heterostructure. Numerical calculation of the band diagram of the graded heterostructure, which is reported, indicates that the contact resistance may be strongly affected by the grading width as well as the exact distribution of the doping level across the heterostructure.