The Role of Air Adsorption in Inverted Ultrathin Black Phosphorus Field-Effect Transistors.

Qianqian Li,Shupeng Wang,Zhihong Feng,Liefeng Feng,Jiancui Chen,Dongsheng Yao

doi:10.1186/s11671-016-1737-6

Abstract

Few-layer black phosphorus (BP) attracts much attention owing to its high mobility and thickness-tunable band gap; however, compared with the commonly studied transition metal dichalcogenides (TMDCs), BP has the unfavorable property of degrading in ambient conditions. Here, we propose an inverted dual gates structure of ultrathin BP FET to research the air adsorption on BP. In fabrication process of back-gate BP FET, BP was transferred directly onto a wafer covered with electrodes. Thus, we can exclude the BP degradation during the process of electrodes fabrication, such as electron beam lithography (EBL) and thermal evaporation process. Furthermore, without any electrode covering BP, BP could be in full contact with the air; then the accurate effect of the air adsorption on BP can be researched in detail. The results clearly show that annealing can remove the p-doping resulted from the metastable oxygen adsorbed on the surface of BP, but the adsorption can be restored in a few hours exposure. In addition, both back and top gate inverted BP FETs exhibit a favorable performance. Therefore, this inverted structure is also an optional structure to reduce the influence of the instability of BP devices.

Highlights

Phosphorus is the second discovered monotypic Van der Waals two-dimensional (2D) material
In fabrication process of back-gate black phosphorus (BP) Field-effect transistors (FET), the BP was transferred directly onto a wafer covered with electrodes
In traditional FET, the electrodes are fabricated on BP directly

Summary

Introduction

Phosphorus is the second discovered monotypic Van der Waals two-dimensional (2D) material. The degradation of BP during the EBL and the thermal evaporation process could be eliminated It can ensure sufficient contact between the air condition and BP because the effect of electrodes covering on BP is avoided. If the device had been fabricated into the traditional structure in our fabrication process, the electrodes should have covered more than half effect area of BP. Both advantages ensure that we could clearly observe the change process of the dominant carrier type.

Methods

Results

Conclusion