Growth of MoS2–Nb-doped MoS2 lateral homojunctions: A monolayer p–n diode by substitutional doping

Mitsuhiro Okada,Naoka Nagamura,Naoya Okada,Yasunobu Ando,Tarojiro Matsumura,Toshitaka Kubo,Anh Khoa Augustin Lu,Toshifumi Irisawa,Tetsuo Shimizu,Wen-Hsin Chang,Takeshi Nakanishi,Takatoshi Yamada

doi:10.1063/5.0070333

Abstract

Monolayer transition metal dichalcogenides (TMDs) have been considered as promising materials for various next-generation semiconductor devices. However, carrier doping techniques for TMDs, which are important for device fabrication, have not been completely established yet. Here, we report a monolayer p–n junction formed using in situ substitutional doping during chemical vapor deposition (CVD). We synthesized monolayer MoS2–Nb-doped MoS2 lateral homojunctions using CVD and then characterized their physical and electrical properties. The optimized growth condition enabled us to obtain spatially selective and heavy Nb doping in the edge region of a single-crystalline MoS2, thus resulting in an obvious work function difference between the inner and edge regions of the crystal. The obtained monolayer crystal demonstrated n-type and degenerate p-type semiconducting behaviors in each region, and a clear rectifying behavior across the n-type and p-type interface was observed. We believe that the results obtained can expand the research field of exploring two-dimensional homo p–n junctions, which can be important for realizing various TMD-based devices, such as diodes and field-effect transistors, with low-contact resistance.

Highlights

We report a monolayer p–n junction formed using in situ substitutional doping during chemical vapor deposition (CVD)
We believe that the results obtained can expand the research field of exploring two-dimensional homo p–n junctions, which can be important for realizing various transition metal dichalcogenides (TMDs)-based devices, such as diodes and field-effect transistors, with low-contact resistance
Even in monolayer limits, TMDs demonstrate excellent carrier mobility and a high on/off ratio when used in field-effect transistors (FETs), making them promising next-generation semiconductor materials

Summary

Introduction

The recent development of two-dimensional (2D) layered transition metal dichalcogenides (TMDs) has opened a new research field for nanotechnology.1,2 In particular, 1H-phase monolayer MoS2, MoSe2, WS2, and WSe2 are direct-gap 2D semiconductors with a bandgap of 1.5–2.0 eV, which is an important feature for developing various optoelectronic devices, such as light-emitting scitation.org/journal/apm devices and photodetectors.3–6 even in monolayer limits, TMDs demonstrate excellent carrier mobility and a high on/off ratio when used in field-effect transistors (FETs), making them promising next-generation semiconductor materials.7,8In general, as-grown TMDs tend to be p- or n-type semiconductors even without intentional doping because of the defects formed and their energy levels.9–11 For example, MoS2 and WS2 show strong n-type behaviors because of the heavy electron doping caused by surface sulfur vacancies.12–15 at the metalelectrode–sulfur-based-TMD interface, there is strong Fermi-level pinning close to the conduction band minimum with a pinning factor of 0.11–0.15, which is attributed to the sulfur vacancies and the metal–chalcogen interactions, resulting in the difficulty of hole injection.16–18 These properties of sulfur-based TMDs make their p-type operation challenging, hindering the formation of lateral homojunctions such as monolayer TMD-based p–n diodes.

Results

Conclusion