Germanane MOSFET for Subdeca Nanometer High-Performance Technology Nodes

Ballistic transport in monolayer Germanane MOSFETs is investigated for high-performance (HP) applications. Characteristics of both n- and p-type transistors having channel lengths of 7, 5, and 3 nm are studied and compared against the International Technology Roadmap for Semiconductor (ITRS) target of 2028. Our simulation approach is based on a self-consistent quantum ballistic transport model within the framework of the nonequilibrium Green's function formalism and relies on a single-band and a two-band k·p Hamiltonian for n- and p-type channels, respectively. We found that, even for a gate length scaled down to 3 nm, the ON current (I_ON) in n- and p-MOSFETs for a fixed OFF current I_OFF =100 nA/μm is as high as ~890 and 700 μA/μm, respectively. For longer channel lengths, the p-MOSFET can outperform the n-MOSFET in terms of I_ON equirements, as the direct source-to-drain tunneling gets suppressed. Other performance metrics, including gate capacitance, intrinsic switching delay, and switching energy, have also been calculated and found to be comparable to the ITRS 2028 HP technology requirements.

I. Introduction

In recent times, atomically thin 2-D materials are being extensively explored as an alternative channel material for transistor technologies able to meet Moore’s law projections in the long-term future. Most of these materials, e.g., graphene, hBN, phosphorene, transition metal dichalcogenides (TMD), such as MoS₂, WS₂, MoSe₂, WSe₂, MoTe₂, and so on [1]–[9], are naturally available in layered form, where 2-D platelets are weakly bonded by van der Waals forces to form 3-D crystals. In an alternate route, recent efforts are also observed to extract 2-D analogues from conventional bulk semiconductors, such as Si, Ge, and GaN [10]–[15]. Among these materials, germanane, a hydrogenated monolayer of germanium, has attracted much attention. Unlike TMDs, which show higher bandgap and higher effective mass, Germanane inherits a very interesting property of having low effective mass along with a relatively high bandgap [15]. From recent first principle-based assessments [16], it was further concluded that chair morphology of Germanane has better potential for conventional and tunnel FET applications than its boat morphology. Stable structure of Germanane has been reported for the first time in 2013 [15], and later used for fabrication of Schottky diodes and FETs [17]–[19].