Formation of low and stable ohmic contacts to GaTe layered crystal

Abstract

In this paper, we report on a systematic study of the formation of ohmic contacts to a GaTe layered crystal grown by the directional freezing method. In this study, the transmission line method (TLM) was used for the measurement of specific contact resistance of ohmic contacts to GaTe. We used In, Au, Al and Ag metals and Au–In eutectic alloy as contact elements. A ladder pattern was formed directly on the GaTe surface by evaporation of metals through a pre-patterned shadow mask. The lowest ohmic contact resistance, 2.5 ± 1.4 × 10−5 ohm cm2, was achieved by annealing In at 200 °C for 2.5 min. Ohmic contacts fabricated by this process remained very stable up to six months after the anneal, although In contacts on some other samples, processed at 175–250 °C for 2.5–14 min, and having higher contact resistance, were unstable. The other elements used in this study showed rectification behaviour after annealing at 175–400 °C for 5 min. X-ray diffraction measurements showed that InGaTe2 formation at the In/GaTe interface was minimized for the sample annealed with the optimum process. We found that the formation of InTe was essential for the successful production of ohmic contacts, and that the quality of the contacts was determined by the competition between InTe and InGaTe2.