Characterization of Ohmic Metal/Hg1-xCdxTe Contacts for Infrared Detection

In this work, metal contacts are fabricated on a p-type Hg1-xCdxTe semiconductor, with composition x = 0.30 and acceptor mercury vacancy concentration in the range of 10(16) cm(-3), by two different technological processes. Depending on the fabrication process, either non-ohmic contacts, with highly nonlinear current-voltage I(V) characteristics, or ohmic contacts are obtained. Different test patterns are measured at variable temperatures down to 77 K. Isolated small-area contacts, comparable to those in focal plane arrays (FPAs), are used to characterize the metal/semiconductor Schottky barrier energy, while transfer length method (TLM) structures are used to estimate the contact specific resistivity of the ohmic contacts. Classical circular TLM (CTLM) patterns are studied and, in addition, new patterns, referred to as variable-width closed TLM (VW-CTLM), are proposed. The linear I(V) characteristics, measured at variable temperatures down to 77 K, demonstrate that high-performance true ohmic contacts on p-type Hg1-xCdxTe can be obtained. To our knowledge, the contact specific resistivity values for these contacts, in the range 0.7-1.8 x 10(-4) ohms cm(2) at 77 K, are lower than the published state-of-the-art values. The very stable values of contact resistance over the whole temperature range is coherent with a dominant pure tunnel conduction mechanism through the metal/Hg1-xCdxTe barrier. TLM is used to analyze the ohmic contacts, and in some cases is used to obtain useful information even on some of the non-ohmic contacts, which is somewhat unusual and possibly innovative.