Layered material GeSe and vertical GeSe/MoS2 p-n heterojunctions

TL;DR

This paper investigates the anisotropic electronic properties of layered GeSe and its heterostructures with MoS2, revealing potential for advanced electronic and optoelectronic devices through experimental and theoretical analysis.

Contribution

It provides the first detailed experimental and theoretical study of GeSe's band structure, transport properties, and heterojunctions with MoS2, highlighting its anisotropic conductance and device potential.

Findings

GeSe exhibits highly anisotropic conductance with maximum along the armchair direction.

Density functional theory shows effective mass is 2.7 times larger along zigzag than armchair.

GeSe/MoS2 heterojunctions have a type-II band alignment with a conduction band offset of ~0.234 eV.

Abstract

Group-IV monochalcogenides are emerging as a new class of layered materials beyond graphene, transition metal dichalcogenides (TMDCs), and black phosphorus (BP). In this paper, we report experimental and theoretical investigations of the band structure and transport properties of GeSe and its heterostructures. We find that GeSe exhibits a markedly anisotropic electronic transport, with maximum conductance along the armchair direction. Density functional theory calculations reveal that the effective mass is 2.7 times larger along the zigzag direction than the armchair direction; this mass anisotropy explains the observed anisotropic conductance. The crystallographic orientation of GeSe is confirmed by angleresolved polarized Raman measurements, which are further supported by calculated Raman tensors for the orthorhombic structure. Novel GeSe/MoS2 p-n heterojunctions are fabricated, combining the natural p-type doping in GeSe and n-type doping in MoS2. The temperature dependence of the measured junction current reveals that GeSe and MoS2 have a type-II band alignment with a conduction band offset of ~0.234 eV. The anisotropic conductance of GeSe may enable the development of new electronic and optoelectronic devices, such as high-efficiency thermoelectric devices and plasmonic devices with resonance frequency continuously tunable through light polarization direction. The unique GeSe/MoS2 p-n junctions with type-II alignment may become essential building blocks of vertical tunneling field-effect transistors for low-power applications. The novel p-type layered material GeSe can also be combined with n-type TMDCs to form heterogeneous complementary metal oxide semiconductor (CMOS) circuits.