Self-Assembled Layer (SAL)-Based Doping on Black Phosphorus (BP) Transistor and Photodetector

Abstract

Black phosphorus (BP) is appealing as a next-generation two-dimensional (2D) van der Waals (vdW) material, but research into doping BP to optimize device performance is still deficient. Here, we study n- and p-doping of variously thick (2, 4, 7, and 10 nm) black phosphorus (BP) films in terms of the performance of the corresponding BP-based transistors and photodetectors. N- and p-doping were respectively achieved with 3-amino-propyltriethoxysilane (APTES) and octadecyltrichlorosilane (OTS). The changed concentrations of BP were between approximately −2.1 × 1011 and −4.82 × 1011 cm–2 for APTES (n-doping) and between 1.06 × 1011 and 1.96 × 1011 cm–2 for OTS (p-doping). In the transistor devices formed on a 2 nm thick BP film, n-doping negatively shifted the threshold voltage from 28.3 to 19.5 V. Conversely, after p-doping with OTS, the threshold voltage was positively shifted from 20.6 to 23.7 V. In the BP photodetectors (2 nm thick devices), responsivity (R) was reduced by −16% (520 nm) and −9% (850 nm) after n-doping, whereas p-doping improved the responsivity by 40% (520 nm) and 20% (850 nm). Through this doping study, the very high photoresponsivity of 1.4 × 104 A/W under 520 nm laser exposure was achieved in 10 nm thick BP/OTS photodetectors. In addition, the n- and p-doping effects were more obvious in thin BP films.