Tunable Schottky barriers in ultrathin black phosphorus field effect transistors via polymer capping

Abstract

It is still a great challenge to avoid the degradation of ultrathin black phosphorus (BP) since its discovery in 2014. Various methods have been explored to stabilize the properties of ultrathin BP through capping technology or chemical passivation. Besides, the large metal-semiconductor contact resistance is also one of the critical issues. The two problems hinder the further development of ultrathin BP devices. Herein, we demonstrate that polymethyl methacrylate (PMMA) capping can not only enhance the durability of the ultrathin BP effectively and nondestructively, but also tune the effective Schottky barriers (SBs) formed at the interfaces between the metal and semiconductor dramatically. Particularly, the Schottky barrier (SB) for electron injection from metal to semiconductor is decreased by ~13 meV and the performance of the BP field effect transistor (FET) is strongly enhanced with the current on/off ratio increased by 6.8 times for the hole conduction after the PMMA capping. In addition, after the electron beam irradiation to the PMMA layer, the charge neutral point of the BP FET exhibits remarkable negative shift resulting in the electron dominated semiconductor channel at zero gate voltage. Furthermore, through partially capping the BP channel, a prototype of BP p-n diode was demonstrated with a maximum rectification factor of 21.3. The diode performs quite well with just a quarter of the BP channel capped by the PMMA layer. Our findings suggest that the PMMA capped ultrathin BP would be a promising choice for future device applications.

Photogating-Induced Controlled Electrical Response in 2D Black Phosphorus

“…Beyond the CNP [III to IV], the drain current ( I d ) starts increasing as the system becomes n-type because of excessive electron doping. In dark condition, the minimum drain current is observed for applied gate voltage at V g = 58.5 V (Figure a), which is the CNP of the BP FET and matches well with the previously reported results of BP. ,− However, under laser illumination, a significant shift in CNP toward the lower (but positive) V g is observed. With the increase in laser power from 0.17 to 22.63 mW, the CNP seems to lower further (inset of Figure a).…”

Memory effects in black phosphorus field effect transistors

“…The transistor covered with PMMA has a slightly larger hysteresis because PMMA can contribute to charge trapping. Indeed, it has been reported by Li et al [58] that the PMMA layer induces positive fixed charges at the interface that need to be balanced by an equal amount of charges with opposite sign in the BP. This process leads to a reduction of the effective Schottky barrier for electrons and to an increase of the effective Schottky barriers for holes, resulting in a negative shift of the charge neutral point and a reduction of the OFF state drain current.…”

Strategies and Applications for Improving the Stability of Black Phosphorus in Physical Environment

“…[ 62 ] In addition, Li et al demonstrated that the polymethyl methacrylate (PMMA) cap could effectively and nondestructively improve the durability of the ultrathin BP. [ 65 ]…”