# Ohmic contact engineering in few-layer black Phosphorus field effect transistors

## TL;DR

This study compares different metal contacts for black phosphorus transistors, finding nickel provides the best Ohmic contact with low resistance and consistent performance across devices.

## Contribution

It systematically evaluates the impact of Chromium, Titanium, and Nickel contacts on black phosphorus transistors, highlighting Nickel's superior contact properties.

## Key findings

- Nickel yields the lowest contact resistance.
- All metals show good linearity in accumulation regime.
- Ni provides consistent performance across devices.

## Abstract

Achieving good quality Ohmic contacts to van der Waals materials is a challenge, since at the interface between metal and van der Waals material, different conditions can occur, ranging from the presence of a large energy barrier between the two materials to the metallization of the layered material below the contacts. In black phosphorus (bP), a further challenge is its high reactivity to oxygen and moisture, since the presence of uncontrolled oxidation can substantially change the behavior of the contacts. In this study, we investigate the influence of the metal used for the contacts to bP against the variability between different flakes and different samples, using three of the most used metals as contacts: Chromium, Titanium, and Nickel. Using the transfer length method, from an analysis of ten devices, both at room temperature and at low temperature, Ni results to be the best metal for Ohmic contacts to bP, providing the lowest contact resistance and minimum scattering between different devices. Moreover, we investigate the gate dependence of the current-voltage characteristics of these devices. In the accumulation regime, we observe good linearity for all metals investigated.