Mott barrier behavior of metal-TlGaSe2 layered semiconductor junction

Abstract

We report on the characteristics of metal-p-type high resistance TlGaSe2 semiconductor junction barrier fabricated by deposition of indium and gold metals. The electrical properties of /TlGaSe2/ semiconductor contacts were monitored as a function of temperature in the range of similar to 80-300 K using current-voltage (I - V) and capacitance-voltage (C - V) measurements. Device characteristics of In/TlGaSe2/Au showed rectification properties. From forward bias I - V characteristics it was revealed that the increase of current is slower than the predictions by Schottky barrier theory. The rectification properties of In/TlGaSe2/Au semiconductor device were simulated by the Mott barrier model where the presence of an undoped layer on the semiconductor surface is assumed, and measurements and computational simulation agreed on the validity of this model. C - V measurements showed that at higher temperatures In/TlGaSe2/Au barrier showed a capacitance from accumulation toward depletion mode, whereas at low temperatures the barrier capacitance degradation was found. The observed C - V of In/TlGaSe2/Au does not significantly change over the entire bias range +/- 30 V, confirming that the In/TlGaSe2/Au is fully depleted, thus the structures are Mott barrier. First-principles electronic band diagram calculations showed that introduction of Se-atom vacancies in the various sites of TlGaSe2 unit cell greatly affects the electronic band structure of this semiconductor in an increasing manner in band gaps with respect to stoichiometric compound. Consequently, the Se - vacancies localized inside the thin surface layer of TlGaSe2 are responsible for high average surface electrical resistivity of the material and could be proposed as a physical basis for the existence of native insulator layer on TlGaSe2 surface. Thus we propose a model for TlGaSe2 crystal which is comprised from an electrically conducting bulk semiconductor sandwiched between two high resistivity thin surface sheets. We suggest that the selenium vacancy defects on the surface of TlGaSe2 layered semiconductor are also responsible for the memristive behavior of this compound.