Highly-stable black phosphorus field-effect transistors with low density of oxide traps

Abstract

Black phosphorus is considered a very promising semiconductor for two-dimensional field-effect transistors. Initially, the main disadvantage of this material was thought to be its poor air stability. However, recent studies have shown that this problem can be solved by suitable encapsulation. As such, long-term studies of the outstanding properties of black phosphorus devices have become possible. In particular, here we examine highly-stable black phosphorus field-effect transistors and demonstrate that they can exhibit reproducible characteristics for at least 17 months. Furthermore, we notice some improvement in the performance of black phosphorus devices after this long time, i.e., positive aging. Although our black phosphorus devices are stable at room temperature, we show that their performance is affected by thermally activated charge trapping by oxide traps into the adjacent SiO2 substrate layer. Aiming to analyze the dynamics of these defects in detail, we perform an accurate mapping of oxide traps with different time constants using the ‘extended incremental hysteresis sweep method’. Our results show that at room temperature the extracted oxide trap densities are (i) few orders of magnitude lower than for MoS2/SiO2 transistors and (ii) close to those reported for more mature Si/SiO2 devices (~1017 cm−3 eV−1). Taking into account the novelty of black phosphorus and recent issues with its stability, these values must be considered unexpectedly low.