Performance Limit Projection of Germanane Field-Effect Transistors

Abstract

Abstract-Here we explore the performance limit of monolayer germanane (GeH) field-effect transistors (FETs). We first plotted an electronic band structure of GeH using density functional theory (DFT) and then tight-binding parameters were extracted. Device characteristics of GeH FETs are investigated using rigorous self-consistent atomistic quantum transport simulations within tight-binding approximations. Our simulation results indicate that GeH FETs can exhibit exceptional on-state device characteristics such as high I on (>2 mA/µm) and large g m (~7 mS/µm) with V DD = 0.5 V due to the very light effective mass of GeH (0.07m 0 ), while maintaining excellent switching characteristics (SS ~64 mV/dec). We have also performed a scaling study by varying the channel length, and it turned out that GeH FET can be scaled down to ~14 nm channel without facing significant short channel effects but it may suffer from large leakage current at the channel length shorter than 10 nm. channel material have rarely explored although it has great potential for future electronic devices toward various applications. The performance of GeH FET was estimated previously by semi-classical model [10], but such a simple approach can be significantly limited in predicting the detailed characteristics of germanane device, where quantum-mechanical treatment will be critical to discuss tunneling and scaling. Therefore, in this work, we investigate the performance limit of GeH FET using rigorous self-consistent atomistic quantum transport simulations. Our simulation results exhibit superior on-state characteristics of GeH FET with excellent switching behaviors. However, due to the very light effective mass, the scaling of GeH FET can be significantly limited as it suffers from large leakage current. We have also benchmarked GeH FET against MoS 2 counterpart, which indicates that GeH FET has clear benefits for high-performance applications compared to a similar device based on MoS 2 . II. SIMULATION METHODSDensity functional theory (DFT) calculation [11] was utilized to obtain the band structure of GeH. Generalized gradient approximations (GGA) exchange correlation function using PBE parameterization was employed for the DFT calculation. For a geometry optimization, conjugate-gradients (CG) was used with maximum force tolerance of 10 -3 eV/Å and energy tolerance of 10 -4 eV. The unit cell of germanane contains two germanium atoms and two hydrogen atoms as shown in the inset of Fig. 1 (a). The Brillouin zone sampling was done using Monkhorst-Pack approach with a 50×50×1 mesh. The calculated band structure is shown in Fig. 1(a This is the author's version of an article that has been published in this journal. Changes were made to this version by the publisher prior to publication.The final version of record is available at http://dx

Insulators for 2D nanoelectronics: the gap to bridge

“…At a first glance, 2D materials seem to allow the arbitrary stacking of different material layers using van der Waals attractive forces 24 . Theoretical calculations have predicted excellent properties for devices built from 2D materials 25 . Also, considerable progress has been made in addressing fabricationrelated issues 26,27 and tuning electrical figures of merit, such as carrier mobility 16,28 and on/off current ratios 14,29 .…”

Assessment of Germanane Field-Effect Transistors for CMOS Technology

“…This is attributed mainly to the smaller DOS of n-type GeH, making the modulation of potential barrier by the gate easier. Although charge density in NMOS is limited by its small DOS, NMOS exhibits larger I on than PMOS due to fact that the gain in the carrier velocity overcomes the loss in charge density [8]. Notably, high carrier velocity in NMOS is the result of both large injection velocity (as shown in the inset of Fig.…”

“…Electronic properties of GeH are described by TB parameters, which have been achieved through numerical fitting of the DFT band structure [8]. Transport properties are simulated based on the non-equilibrium Green's function (NEGF) method within a TB approximation, while self-consistent electrostatic potential is achieved by solving the Poisson's equation alongside the transport equation [11] , where it can be seen that electrons have significantly higher velocity than holes.…”

“…GeH is a light-effective-mass material (m e * < 0.1m 0 ), and an exceptionally high carrier mobility (>18,000 cm 2 /V•s) is theoretically predicted [4], while measured mobility of GeH field-effect transistor (FET) is still limited to much lower values (30 cm 2 /V•s) [7]. With regard to device performance, promising characteristics of GeH FETs have been predicted for high-performance applications [8]- [10]. Although n-type GeH FETs have been carefully investigated based on atomistic quantum transport simulations [8], in-depth understanding of p-type GeH device is currently absent from the field.…”

“…With regard to device performance, promising characteristics of GeH FETs have been predicted for high-performance applications [8]- [10]. Although n-type GeH FETs have been carefully investigated based on atomistic quantum transport simulations [8], in-depth understanding of p-type GeH device is currently absent from the field. Notably, GeH has heavy holes and light holes, which cannot be captured with semi-classical models [10].…”