OHMIC AND BARRIER CONTACTS ON NARROW-GAP SEMICONDUCTORS (REVIEW)

A systematic review of the mechanisms of Schottky barrier formation and electrical properties of metal contacts on narrow-gap semiconductors (NGS) (HgCdTe, InSb, InAs) has been performed. The relevance of such an analysis is explained by the fact that the electronic structure of metal/NGS interfaces, as well as the electrical properties of contacts, are still poorly understood. This is evident from the large number of models proposed to explain the position of the Fermi level at the transition boundary, including the Schottky work function model and the modified Friouf and Woodall work function model, Bardeen surface states, metal-induced gap states, and Spicer intrinsic defects. It has been shown that the formation of Schottky barriers is influenced by several phenomena, including surface preparation, chemical reactions, interdiffusion at the interface, and doping of the near-surface semiconductor layer with a contact metal. The importance of chemical reactions for the barrier formation seems to be recognized for all NGS. Chemical reactions of the metal with the cations and anions of the semiconductor produce new species at the interface that can affect the electrical properties of the contacts. For example, the width of the interface is a function of the heat of reaction of the metal with the semiconductor anion. An abrupt interface is formed at contacts where the metal-anion interaction is strong, while interdiffusion is observed for non-reactive contacts. The metal/HgCdTe system differs from other NGS in that interfacial reactions lead to the loss of Hg at the interface, which was shown by ultraviolet and X-ray photoemission spectroscopy on cleaved surfaces in an ultrahigh vacuum environment. However, the relationship between the reactivity of metal/HgCdTe contacts, as well as contacts with other NGS, and their electrical properties requires further investigation. Also, the effect of surface oxide on barrier formation in these contacts may differ significantly from that observed in contacts on A3B5 semiconductors. In summary, based on previously conducted studies, recommendations can be offered for the fabrication of ohmic and barrier contacts on n- and p-type materials.