In situ thickness control of black phosphorus field-effect transistors via ozone treatment

A simple and reproducible method to control the thickness of black phosphorus flakes in real time using a UV/ozone treatment is demonstrated. Back-gated black phosphorus field-effect transistors (FETs) were fabricated using thick black phosphorus flakes obtained by thinning of black phosphorus, as oxygen radicals generated by UV irradiation formed phosphorus oxides on the surface. In order to monitor the thickness effect on the electrical properties, the fabricated FETs were loaded in the UV/ozone chamber, where both the optical (micro-Raman spectroscopy and optical microscopy) and electrical properties (current-voltage characteristics) were monitored in situ. We observed an intensity decrease of the Raman modes of black phosphorus while the field-effect mobility and on/off ratio increased by 48% and 6,800%, respectively. The instability in ambient air limits the investigation and implementation of ultra-thin black phosphorus. However, the method reported in this study allowed us to start with thick black phosphorous flakes, providing a reliable approach for optimizing the electrical performance of black phosphorus-based electronic devices. We believe that these results can motivate further studies using mono- and few-layer black phosphorus.