Atomic Structure and Electrical Properties of In(Te) Nanocontacts on CdZnTe(110) by Scanning Probe Microscopy

Understanding complex correlations between the macroscopic device performance (largely dependent on the character of the metal-semiconductor contact) and the metallurgy of contact formation on the atomic level in cadmium zinc telluride (CdZnTe) radiation detectors remains a formidable challenge. In this work, an effort towards bridging that macro-nano knowledge gap is made by conducting a series of controlled experiments aimed at correlating electrical properties of the In contact to n-type CdZnTe(110) surface with the step-by-step process of contact formation. This can only be achieved by using high spatial resolution techniques, capable of conducting highly localized measurements on the nano- and sub-nanoscale, such as scanning probe microscopy. Scanning tunneling microscopy is used in situ to monitor the behavior of various In atom coverages on an atomically flat and ordered CdZnTe surface under well-controlled molecular beam epitaxial conditions in ultra-high vacuum. Electrical derivatives of atomic force microscopy are used to measure the electrical contact properties, such as contact potential difference and spreading resistance in torsion resonance tunneling mode. It is concluded that In atoms preferentially reacted with Te atomic-rows already at room temperature, forming nanometric patches of indium-telluride Schottky-type contacts. The methods developed in this study, in terms of both nanocontact fabrication and characterization (especially in terms of electrical properties) should benefit basic and applied research of any metal-semiconductor system.