[Paper Review] Simulation of Schottky-Barrier Phosphorene Transistors

Runlai Wan, Xi Cao+1 more|arXiv (Cornell University)|Aug 21, 2014

2D Materials and Applications11 references3 citations

TL;DR

This study simulates Schottky-barrier phosphorene field-effect transistors using the non-equilibrium Green's function formalism, revealing that thin gate oxides induce strong ambipolar leakage, especially in thicker phosphorene layers. The key finding is that monolayer or bilayer phosphorene effectively suppresses leakage and enables high ON-current, with performance strongly dependent on crystallographic direction due to anisotropic transport properties.

ABSTRACT

Schottky barrier field-effect transistors (SBFETs) based on few and mono layer phosphorene are simulated by the non-equilibrium Green's function formalism. It is shown that scaling down the gate oxide thickness results in pronounced ambipolar I-V characteristics and significant increase of the minimal leakage current. The problem of leakage is especially severe when the gate insulator is thin and the number of layer is large, but can be effectively suppressed by reducing phosphorene to mono or bilayer. Different from two-dimensional graphene and layered dichalcogenide materials, both the ON-current of the phosphorene SBFETs and the metal-semiconductor contact resistance between metal and phosphorene strongly depend on the transport crystalline direction.

Motivation & Objective

• To investigate the performance limits of Schottky-barrier field-effect transistors (SBFETs) based on few- and single-layer phosphorene.
• To analyze the impact of gate oxide thickness and number of phosphorene layers on leakage current and ambipolar behavior.
• To evaluate the role of crystallographic direction in determining ON-current and contact resistance in phosphorene SBFETs.
• To compare phosphorene SBFETs with graphene and transition metal dichalcogenide devices in terms of leakage and anisotropy.

Proposed method

• The non-equilibrium Green's function (NEGF) formalism is used to model electron transport in phosphorene SBFETs.
• Simulations are performed for few- and single-layer phosphorene with varying gate oxide thicknesses.
• The model accounts for Schottky barrier formation at the metal–phosphorene interface.
• Anisotropic band structure and transport properties are incorporated based on phosphorene's layered crystal structure.
• Current–voltage (I–V) characteristics are computed in both source–drain and gate configurations to assess ambipolar behavior.
• Contact resistance between metal and phosphorene is evaluated as a function of crystallographic direction.

Experimental results

Research questions

• RQ1 How does gate oxide thickness affect leakage current and ambipolar behavior in phosphorene SBFETs?
• RQ2 What is the impact of the number of phosphorene layers on the minimal leakage current and ON-current?
• RQ3 How does the crystallographic direction influence the ON-current and metal–semiconductor contact resistance in phosphorene SBFETs?
• RQ4 How do phosphorene SBFETs compare to graphene and dichalcogenide-based SBFETs in terms of leakage and anisotropy?

Key findings

• Reducing gate oxide thickness significantly increases leakage current and induces pronounced ambipolar I–V characteristics.
• Thick phosphorene layers (multilayer) exhibit severe leakage when the gate oxide is thin, limiting device performance.
• Monolayer and bilayer phosphorene effectively suppress leakage and maintain high ON-current, even with thin oxides.
• The ON-current in phosphorene SBFETs is strongly anisotropic, depending on the crystallographic transport direction.
• Metal–phosphorene contact resistance also varies significantly with crystallographic direction, affecting overall device efficiency.
• Phosphorene SBFETs show stronger anisotropy in both current and contact resistance than graphene or dichalcogenide-based devices.