Large-Area Pulsed Laser Deposited Molybdenum Diselenide Heterojunction Photodiodes

Abstract

Two-dimensional (2D) semiconductors, such as transition-metal dichalcogenides (TMDs), have attracted immense interest due to their excellent electronic and optical properties. The combination of single and multilayered 2D TMDs coupled with either Si or II–VI semiconductors can result in robust and reliable photodetectors. In this paper, we report the deposition process of MoSe2-layered films using pulsed laser deposition (PLD) over areas of 20 cm2 with a tunable band gap. Raman and X-ray diffraction indicates crystalline and highly oriented layered MoSe2. X-ray photoelectron spectroscopy shows Mo and Se present in the first few layers of the film. Rutherford backscattering demonstrates the effect of O and C on the surface and film/substrate interface of the deposited films. Ultraviolet–visible spectroscopy, Kelvin probe, photoelectron spectroscopy, and electrical measurements are used to investigate the band diagram and electrical property dependence as a function of MoSe2 layers/thickness. As the MoSe2 thickness increases from 3.5 to 11.4 nm, the band gap decreases from 1.98 to 1.75 eV, the work function increases from 4.52 to 4.72 eV, the ionization energy increases from 5.71 to 5.77 eV, the sheet resistance decreases from 541 to 56.0 kΩ, the contact resistance decreases from 187 to 54.6 Ω·cm2, and the transfer length increases from 2.27 to 61.9 nm. Transmission electron microscopy (TEM) cross-sectional images demonstrate the layered structure of the MoSe2 with an average interlayer spacing of 0.68 nm. The fabricated MoSe2–Si photodiodes demonstrate a current on/off ratio of ∼2 × 104 orders of magnification and photocurrent generation with a 22.5 ns rise time and a 190.8 ns decay time, respectively.

Recent progress on Schottky sensors based on two-dimensional transition metal dichalcogenides

“…91 It has been reported that a high laser energy density and temperature contribute to the high crystalline orientation of the resulting films, and the stoichiometry and purity of the films can be changed by adjusting the pressure and environment in the deposition chamber. 92…”

Toward Wafer‐Scale Production of 2D Transition Metal Chalcogenides

“…Especially, the stoichiometry of the deposit materials could be retained well because the target species are transferred congruently through laser ablation, in the ultrahigh vacuum. [118,165,166] Seo et al reported growth of continuous WSe 2 film through PLD, in the scale of 1 cm × 1 cm. They varied the number of pulses, and obtained various thickness from monolayer to trilayers (Figure 10b) with a high uniformity and homogeneity, demonstrated by the Raman mapping of the E 1 2g and A 1g modes and the root-mean-square (RMS) roughness of 0.26-0.29 nm.…”

Mixed-Dimensional InSe–Si Heterojunction Nanostructures for Self-Powered Broadband Photodetectors

“…The current ( I )–voltage ( V ) curves of the InSe–Si heterojunction are displayed in Figure a. The vdWHs show a significant rectifying effect with a large rectification ratio (RR) of 5000 at small bias voltages of ±1 V. As shown in Figure b, the RR of the 2D–3D InSe–Si vdWHs is superior to those of all other 2D InSe-based heterojunctions ,,− ,− and is comparable to those of most transition-metal dichalcogenide-based 2D–3D heterojunctions ,, measured without a gate voltage. The ideality factor ( n ) is 1.1, indicating that the diffusion current is responsible for the current rectifying behavior of the InSe–Si vdWHs.…”

“…(a) I - V curves of the InSe-Si vdWHs. (b) Comparison of the RRs of various 2D InSe-based heterojunctions and mixed-dimensional (2D–3D) vdWHs measured without a gate voltage, including InSe–Se, InSe–Te, InSe–AsP, InSe–GaTe, InSe–BP, MoS 2 –InSe, InSe–GaSe, InSe–GeAs, MoS 2 –Si, WS 2 –Si, and MoSe 2 –Si …”