ABSTRACT
Monolayer MoS2 possesses good electron mobility, structural flexibility and a direct band gap, enabling it to be a promising candidate for flexible and wearable optoelectronic devices. In this article, the lateral monolayer MoS2 homojunctions were prepared by a nitrogen plasma selective doping technique. The monolayer MoS2 thin films were synthesized by chemical vapor deposition and characterized by photoluminescence, atom force microscope and Raman spectroscopy. The electronic and photoelectric properties of the lateral pn and npn homojunctions were discussed. The results showed that the rectifying ratio of the pn homojunction diode is â¼103. As a photodetector of pn homojunction, the optical responsivity is up to 48.5 A W-1, the external quantum efficiency is 11 301%, the detectivity is â¼109 Jones and the response time is 20 ms with the laser of 532 nm and the reverse bias voltage of 10 V. As a bipolar junction transistor of npn homojunction, the amplification coefficient reached â¼102. A controllable plasma doping technique, compatible with traditional CMOS process, is utilized to realize the monolayer MoS2 based pn and npn homojunctions, and it propels the potential applications of 2D materials in the electronic, optoelectronic devices and circuits.
ABSTRACT
Monolayer 2H-phase MoS2-based photodetectors exhibit high photon absorption but suffer from low photoresponse, which severely limits their applications in optoelectronic fields. The metallic 1T phase of MoS2, while transporting carriers faster, shows negligible response to visible light, which limits its usage in photodetectors. Herein, we propose an ultrafast-response MoS2-based photodetector having a channel that consists of a 2H-MoS2 sensitizing monolayer on top of 1T@2H-MoS2. The 1T@2H-MoS2 layer has a thickness of several nanometers and is a mixture of metallic 1T-MoS2 and semiconducting 2H-MoS2, imparting metal-like properties to the photodetector. Compared with the monolayer 2H-MoS2 photodetector, we observed a drastic increase in the photoresponse of the 2H-MoS2/1T@2H-MoS2 vertically stacked photodetector to a value of 1917 A W-1. Owing to the presence of metallic 1T-MoS2 within the metal-like 1T@2H-MoS2, the performance of the 2H-MoS2/1T@2H-MoS2 vertically stacked photodetector is voltage bias-modulated with an external quantum efficiency (EQE) of up to 448,384% and a specific detectivity of up to â¼1011 Jones. The higher carrier density and higher mobility of the 1T@2H-MoS2 layer explain the better bias-modulated performance. In addition, the interface between 2H-MoS2 and 1T@2H-MoS2 ensures fewer dangling bonds and reduced lattice mismatching. Thus, this study presents an exclusive vertically stacked MoS2-based photodetector that lays the foundation for the development of photodetectors exhibiting higher photoresponse.
ABSTRACT
Low damaged doping of two-dimensional (2D) materials proves to be a significant obstacle in realizing fundamental devices such as p-n junction diodes and transistors due to its atom layer thickness. In this work, the defect formation energy and p-type conduction behavior of nitrogen plasma doping are investigated by first principle calculation. Low damaged substitutional p-type doping in MoS2 using low energy nitrogen plasma composed of N+ and N2 + is achieved by a novel toroidal magnetic field (TMF). The TMF helps to raise the concentration of N2 + ions at low RF power condition. The electrical characteristics of double-layer MoS2 field-effect transistors (FETs) clearly show an efficient p-type doping behavior. Atomic force microscope is applied to verify the slight damage in MoS2. X-ray photoelectron spectroscopy, photoluminescence and Raman spectroscopy confirm the effective p-type doping characteristic with weak damage. These findings provide a low damage technology for efficient carrier modulation of MoS2 and other homogeneous TMDC materials, which overcomes barriers in developing 2D electronic and optoelectronic devices.
