Ab Initio Quantum Transport Simulations Research Articles

Performance assessment of monolayer Black Phosphorus DG-JLFET

Two-dimensional materials are very promising for ultra-short channel future devices. This paper investigates, for the first time, the viability of the junction less transistors based on 2-D materials for future state-of-the-art technology nodes. Specifically, we investigate the performance of a Junction less monolayer black phosphorus (BP) FET (JLFET) with 12nm gate length using ab initio quantum transport simulations. The electrostatic control mechanism of the device and various intrinsic static and dynamic characteristics of the device are studied. The results reveal that BP JLFET performance can fulfill the benchmark requirement of International Roadmap for Devices and Systems (IRDS 2021) for 2028 in terms of HP and HD applications. Therefore, JLFET based on 2D materials can be a promising alternative for nano scale future device applications.

Sub-5 nm Ultrathin In2O3 Transistors for High-Performance and Low-Power Electronic Applications.

Ultrathin oxide semiconductors are promising candidates for back-end-of-line (BEOL) compatible transistors and monolithic three-dimensional integration. Experimentally, ultrathin indium oxide (In2O3) field-effect transistors (FETs) with thicknesses down to 0.4 nm exhibit an extremely high drain current (104 μA/μm) and transconductance (4000 μS/μm). Here, we employ ab initio quantum transport simulation to investigate the performance limit of sub-5 nm gate length (Lg) ultrathin In2O3 FETs. Based on the International Technology Roadmap for Semiconductors (ITRS) criteria for high-performance (HP) devices, the scaling limit of ultrathin In2O3 FETs can reach 2 nm in terms of on-state current, delay time, and power dissipation. The wide bandgap nature of ultrathin In2O3 (3.0 eV) renders it a suitable candidate for ITRS low-power (LP) electronics with Lg down to 3 nm. Notably, both the HP and LP ultrathin In2O3 FETs exhibit superior energy-delay products as compared to those of other common 2D semiconductors such as monolayer MoS2 and MoTe2. These findings unveil the potential of ultrathin In2O3 in HP and LP nanoelectronic device applications.

Effective self-power photodetector based on photogalvanic effect: A case study for Janus MoSSe-CrSSe lateral heterojunction

The photogalvanic effect (PGE) can produce a photocurrent independent of a p–n junction or bias voltage, but the resulting photocurrent is usually very small. An appropriate lateral heterojunction can effectively enhance PGE. Here, we studied the PGE of a monolayer (ML) Janus MoSSe-CrSSe lateral heterojunction through ab initio quantum transport simulation. Compared with that of a homogeneous material, PGE is enhanced due to the reduced symmetry of the lateral heterojunction, and the maximum increase ratio in the photocurrent is more than two orders of magnitude greater than that of the homogeneous ML MoSSe and CrSSe photodetectors. A peak maximum photocurrent of 13.85 a[Formula: see text]/photon and high polarization sensitivity with a maximum extinction ratio of 308 are obtained for the ML MoSSe-CrSSe lateral heterojunction. These favorable properties indicate that the MoSSe-CrSSe lateral heterojunction is a promising candidate for photodetectors.

Low-Power Transistors with Ideal p-type Ohmic Contacts Based on VS2/WSe2 van der Waals Heterostructures.

Achieving low-resistance Ohmic contacts with a vanishing Schottky barrier is crucial for enhancing the performance of two-dimensional (2D) field-effect transistors (FETs). In this paper, we present a theoretical investigation of VS2/WSe2-vdWHs-FETs with a gate length (Lg) in the range of 1-5 nm, using ab initio quantum transport simulations. The results show that a very low hole Schottky barrier height (-0.01 eV) can be achieved with perfect band offsets and reduced metal-induced gap states (MIGS), indicating the formation of p-type Ohmic contacts. Additionally, these FETs also exhibit an impressive low subthreshold swing (SS) (69 mV/dec) and high Ion/Ioff (>107) with an appropriate underlap (UL) structure consisting of pristine WSe2. Furthermore, even when the Lg is scaled down to 3 nm, the device can still meet the low-power (LP) requirements of the International Technology Roadmap for Semiconductors (ITRS) by controlling the UL. Consequently, this study provides valuable insights for the future development of LP 2D FETs.

Interfacial Properties of Anisotropic Monolayer SiAs Transistors

The newly prepared monolayer (ML) SiAs is expected to be a candidate channel material for next-generation nano-electronic devices in virtue of its proper bandgap, high carrier mobility, and anisotropic properties. The interfacial properties in ML SiAs field-effect transistors are comprehensively studied with electrodes (graphene, V2CO2, Au, Ag, and Cu) by using ab initio electronic structure calculations and quantum transport simulation. It is found that ML SiAs forms a weak van der Waals interaction with graphene and V2CO2, while it forms a strong interaction with bulk metals (Au, Ag, and Cu). Although ML SiAs has strong anisotropy, it is not reflected in the contact property. Based on the quantum transport simulation, ML SiAs forms n-type lateral Schottky contact with Au, Ag, and Cu electrodes with the Schottky barrier height (SBH) of 0.28 (0.27), 0.40 (0.47), and 0.45 (0.33) eV along the a (b) direction, respectively, while it forms p-type lateral Schottky contact with a graphene electrode with a SBH of 0.34 (0.28) eV. Fortunately, ML SiAs forms an ideal Ohmic contact with the V2CO2 electrode. This study not only gives a deep understanding of the interfacial properties of ML SiAs with electrodes but also provides a guide for the design of ML SiAs devices.

Comprehensive understanding of electron mobility and superior performance in sub-10 nm DG ML tetrahex-GeC2 n-type MOSFETs.

In this study, we have investigated the electron mobility of monolayered (ML) tetrahex-GeC2 by solving the linearized Boltzmann transport equation (BTE) with the normalized full-band relaxation time approximation (RTA) using density functional theory (DFT). Contrary to what the deformation potential theory (DPT) suggested, the ZA acoustic mode was determined to be the most restrictive for electron mobility, not the LA mode. The electron mobility at 300 K is 803 cm2 (V s)-1, exceeding the 400 cm2 (V s)-1 of MoS2 which was calculated using the same method and measured experimentally. The ab initio quantum transport simulations were performed to assess the performance limits of sub-10 nm DG ML tetrahex-GeC2 n-type MOSFETs, including gate lengths (Lg) of 3 nm, 5 nm, 7 nm, and 9 nm, with the underlap (UL) effect considered for the first two. For both high-performance (HP) and low-power (LP) applications, their on-state currents (Ion) can meet the requirements of similar nodes in the ITRS 2013. In particular, the Ion is more remarkable for HP applications than that of the extensively studied MoS2. For LP applications, the Ion values at Lg of 7 and 9 nm surpass those of arsenene, known for having the largest Ion among 2D semiconductors. Subthreshold swings (SSs) as low as 69/53 mV dec-1 at an Lg of 9 nm were observed for HP/LP applications, and 73 mV dec-1 at an Lg of 5 nm for LP applications, indicating the excellent gate control capability. Moreover, the delay time τ and power dissipation (PDP) at Lg values of 3 nm, 5 nm, 7 nm, and 9 nm are all below the upper limits of the ITRS 2013 HP/LP proximity nodes and are comparable to or lower than those of typical 2D semiconductors. The sub-10 nm DG ML tetrahex-GeC2 n-type MOSFETs can be down-scaled to 9 nm and 5 nm for HP and LP applications, respectively, displaying desirable Ion, delay time τ, and PDP in the ballistic limit, making them a potential choice for sub-10 nm transistors.

Tunable ohmic van der Waals-type contacts in monolayer C3N field-effect transistors.

Monolayer (ML) C3N, a novel two-dimensional flat crystalline material with a suitable bandgap and excellent carrier mobility, is a prospective channel material candidate for next-generation field-effect transistors (FETs). The contact properties of ML C3N-metal interfaces based on FETs have been comprehensively investigated with metal electrodes (graphene, Ti2C(OH/F)2, Zr2C(OH/F)2, Au, Ni, Pd, and Pt) by employing ab initio electronic structure calculations and quantum transport simulations. The contact properties of ML C3N are isotropic along the armchair and zigzag directions except for the case of Au. ML C3N establishes vertical van der Waals-type ohmic contacts with all the calculated metals except for Zr2CF2. The ML C3N-graphene, -Zr2CF2, -Ti2CF2, -Pt, -Pd, and -Ni interfaces form p-type lateral ohmic contacts, while the ML C3N-Ti2C(OH)2 and -Zr2C(OH)2 interfaces form n-type lateral ohmic contacts. The ohmic contact polarity can be regulated by changing the functional groups of the 2D MXene electrodes. These results provide theoretical insights into the characteristics of ML C3N-metal interfaces, which are important for choosing suitable electrodes and the design of ML C3N devices.

A self-power photodetector based on Janus SnSSe–ZrSSe lateral heterojunction: A theoretical study

The photogalvanic effect (PGE) is attractive for self-powered photodetectors. We study the PGE of lateral Janus SnSSe–ZrSSe photodetectors using ab initio quantum transport simulations. Under the illumination of linearly polarized light, a globally enhanced PGE is found for the lateral SnSSe–ZrSSe photodetector compared to the ML SnSSe and ZrSSe photodetectors. The lateral SnSSe–ZrSSe photodetector exhibits better performance along the armchair direction than its counterpart along the zigzag direction, where a maximum PGE photocurrent of 34 a02/photon at Eph = 5.0 eV and a high extinction ratio of 194 at Eph = 6.0 eV are acquired. Our study suggests that lateral SnSSe–ZrSSe is a promising candidate for ultraviolet photodetectors.

Ohmic contact in two-dimensional WS2/Hf2CX2 (X = F/OH) and WS2/graphene/Hf2C heterojunctions

Low-resistance Ohmic contacts are the key to improving the performance of electronic devices. By performing ab initio electronic calculations and quantum transport simulations, we systematically investigate the contact types of the original WS2/Hf2C, the functionalized WS2/Hf2CX2 (X = F/OH), and the graphene-doped WS2/graphene/Hf2C heterojunctions. The obtained results suggest that the strong interfacial coupling occurs in the WS2/Hf2C system, leading to the metallization of the WS2 layer. Functionalization of the Hf2C layer can significantly weaken the interlayer interactions. Thus, the semiconductor characteristics of the WS2 layer can be maintained in the WS2/Hf2CX2 (X = F/OH) and WS2/graphene/Hf2C heterojunctions. Stable Ohmic contacts are formed in these heterojunctions. The heights of the vertical electron Schottky barrier are −0.13 eV, −0.43 eV, and −0.12 eV for WS2/Hf2CF2, WS2/Hf2C(OH)2, and WS2/graphene/Hf2C, respectively. Based on these heterojunctions, we construct a two-probe field-effect transistor model and explore its quantum transport properties. In the lateral direction, all systems form n-type Schottky contacts. This investigation provides a basis for the selection of electrode materials based on WS2 devices.

Isotropic Contact Properties in Monolayer GeAs Field-Effect Transistors

Owing to the tunable bandgap and high thermodynamic stability, anisotropic monolayer (ML) GeAs have arisen as an attractive candidate for electronic and optoelectronic applications. The contact properties of ML GeAs with 2D metal (graphene, Ti2CF2, V2CF2, and Ti3C2O2) and Cu electrodes are explored along two principal axes in field-effect transistors (FET) by employing ab initio electronic structure calculations and quantum transport simulations. Weak van der Waals interactions are found between ML GeAs and the 2D metal electrodes with the band structure of ML GeAs kept the same, while there is a strong interaction between ML GeAs and the Cu metal electrode, resulting in the obvious hybridization of the band structure. Isotropic contact properties are seen along the two principal directions. P-type lateral Schottky contacts are established in ML GeAs FETs with Ti3C2O2, graphene, and Ti2CF2 metals, with a hole Schottky barrier height (SBH) of 0.12 (0.20), 0.15 (0.11), and 0.29 (0.21) eV along the armchair (zigzag) direction, respectively, and an n-type lateral Schottky contact is established with the Cu electrode with an electron SBH of 0.64 (0.57) eV. Surprisingly, ML GeAs forms ideal p-type Ohmic contacts with the V2CF2 electrode. The results provide a theoretical foundation for comprehending the interactions between ML GeAs and metals, as well as for designing high-performance ML GeAs FETs.

Interfacial electronic states and self-formed asymmetric Schottky contacts in polar α-In2Se3/Au contacts

In recent years, the two-dimensional (2D) semiconductor α-In2Se3 has great potential for applications in the fields of electronics and optoelectronics due to its spontaneous iron electrolysis properties. Through ab initio electronic structure calculations and quantum transport simulations, the interface properties and transport properties of α-In2Se3/Au contacts with different polarization directions are studied, and a two-dimensional α-In2Se3 asymmetric metal contact design is proposed. When α-In2Se3 is polarized upward, it forms an n-type Schottky contact with Au. While when α-In2Se3 is polarized downward, it forms a p-type Schottky contact with Au. More importantly, significant rectification effect is found in the asymmetric Au/α-In2Se3/Au field-effect transistor. The carrier transports under positive and negative bias voltages are found to be dominated by thermionic excitation and tunneling, respectively. These findings provide guidance for the further design of 2D α-In2Se3-based transistors.

Layer-Dependent Magnetoresistance and Spin-Transfer Torque in MnSe2 -Based Magnetic Tunnel Junctions

The recently synthesized two-dimensional van der Waals (vdW) ferromagnet 1T-${\mathrm{MnSe}}_{2}$ has attracted great attention due to its room-temperature ferromagnetism. By using ab initio quantum transport simulations with noncollinear spins, we demonstrate a monotonic increasing (decreasing) tendency of the angle-resolved tunneling magnetoresistance (spin-transfer torque) with the increasing graphene layer number n in the ${\mathrm{MnSe}}_{2}$/n-layer graphene/${\mathrm{MnSe}}_{2}$ (n = 1--4) vdW magnetic tunnel junctions (MTJs). A surprising tunneling magnetoresistance of around ${10}^{6}$% is obtained when $\ensuremath{\theta}={180}^{\ensuremath{\circ}}$ and n = 4 owing to the nearly perfect spin polarization; this is 3 orders of magnitude larger than that of the commonly used $\mathrm{MgO}$-based MTJ (1000% at 5 K). The maximal linear-response spin-transfer torque of the ${\mathrm{MnSe}}_{2}$/graphene/${\mathrm{MnSe}}_{2}$ MTJ (5260 \textmu{}eV/V) is 2 orders of magnitude larger than that of the $\mathrm{Fe}/\mathrm{MgO}/\mathrm{Fe}$ MTJ. The decay rate of the spin-transfer torkance at zero bias is revealed to be nonmonotonically n dependent. Meanwhile, the total spin-transfer torque in the device changes from linear dependence to nonlinear dependence as the bias voltage increases. Our calculation suggests that the 1T-${\mathrm{MnSe}}_{2}$-based vdW MTJs are promising in next-generation room-temperature nonvolatile memories.

Scaling limits of monolayer AlN and GaN MOSFETs

The shrinking of transistors to ultra-scale limits is in great demand to extend Moore’s law, where the search for proper alternative channel materials is significant. The III-V group compounds are regarded as post-Si candidates for their high electron mobility. Herein, we simulate the monolayer (ML) AlN and GaN metal–oxidesemiconductor field-effect transistors (MOSFETs) with ab initio quantum transport simulation to evaluate their scale limit. The ML AlN and GaN MOSFETs exhibit much better n-type performances than their p-type counterparts, and the n-type ML AlN (GaN) MOSFETs can surpass the International Roadmap for Device and Systems (IRDS, 2022 version) lower-power (LP) and high-performance (HP) target for the year 2028 even at gate length (Lg) of 3 and 2 nm, respectively. Encouragingly, the optimal n-type ML AlN (GaN) MOSFETs possess the highest (second-highest) Ion against all studied n-type ML MOSFETs and propel the Lg limit that outperforms the International Technology Roadmap for Semiconductors (ITRS, 2013 version) LP and HP targets to 2 and 1 (2) nm, respectively.

High-Performance FexGeTe2− Based ( x = 4 or 5) van der Waals Magnetic Tunnel Junctions

Recently synthesized two-dimensional (2D) van der Waals (vdW) ferromagnets, ${\mathrm{Fe}}_{x}{\mathrm{Ge}\mathrm{Te}}_{2}$ (x = 4 and 5), have attracted great attention due to their room-temperature Curie temperature. By using ab initio noncollinear-spin quantum transport simulations, we predict a monotonic increasing tendency of the tunneling magnetoresistance (TMR) with increasing \ensuremath{\theta} (the angle between the spins of the two electrodes) in ${\mathrm{Fe}}_{x}{\mathrm{Ge}\mathrm{Te}}_{2}$/graphene/${\mathrm{Fe}}_{x}{\mathrm{Ge}\mathrm{Te}}_{2}$ vdW magnetic tunnel junctions (MTJs). The calculated maximal TMR of the two MTJs is up to 7000% and 1100% for x = 4 and 5, respectively, and the former is even nearly 6 times larger than that of the commonly used $\mathrm{Mg}\mathrm{O}$-based MTJ (1000% at 5 K) owing to nearly perfect spin polarization. The calculated maximal spin-transfer torque per voltage is 1--2 orders of magnitude larger than that of the $\mathrm{Mg}\mathrm{O}$-based one, resulting in a reduction in the critical current for magnetization reversal by a factor of 4--5. Such high-performance 2D ${\mathrm{Fe}}_{x}{\mathrm{Ge}\mathrm{Te}}_{2}$-based (x = 4 and 5) MTJs are promising for next-generation room-temperature nonvolatile memories.

Ferroelectric-Tunable Photoresponse in α- In2Se3 Photovoltaic Photodetectors: An Ab Initio Quantum Transport Study

Two-dimensional \ensuremath{\alpha}-${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ has drawn broad attention due to its high photoresponse and unique room-temperature interlocked in-plane and out-of-plane ferroelectricity with an ultralow switching electric field. Here, we investigate the photoresponse in a lateral monolayer (ML) \ensuremath{\alpha}-${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ p-i-n junction by using ab initio quantum transport simulations. The maximum photoresponses of the lateral \ensuremath{\alpha}-${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ p-i-n junction are up to 69.2 and 31.6 mA/W for the ferroelectric wurtzite and zincblende phases (shortly named WZ' and ZB') \ensuremath{\alpha}-${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$, respectively, which are 8--17 times higher than that of the extensively researched graphene photodetector (4 mA/W). Remarkably, the ferroelectric photoresponses, defined as the photoresponse change ratio between the two ferroelectric states, of the lateral ML WZ' and ZB'-${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ photodetectors have average values of 127% and 121% with surprising maximum values of $2\ifmmode\times\else\texttimes\fi{}{10}^{6}\mathrm{%}$ and $1\ifmmode\times\else\texttimes\fi{}{10}^{7}\mathrm{%}$, respectively. The physical mechanism comes from the electron density redistribution altered by the atomic displacements due to the polarization switch, rather than the built-in potential change induced by the surface polarization charges. Such ferroelectric-tunable photoresponses in the \ensuremath{\alpha}-${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ photodetector suggest a potential in the fabrication of future optical detection and storage integrated devices.

Designing sub-5 nm monolayer AlP MOSFETs

Two dimensional (2D) materials have appealed to great interest for microelectronics in developing the next era of metal-oxide-semiconductor field-effect transistors (MOSFETs). 2D aluminum phosphorous (AlP) with constancy under ambient settings is a suitable channel material for the next MOSFET era. Based on the ab initio quantum transport simulation, we investigate the device performance of the n and p-type sub-5 nm monolayer (ML) AlP MOSFETs. The ML AlP MOSFETs could be satisfied the International Technology Roadmap for Semiconductors (ITRS) standard 2028 by their optimal parameters; on-state current (Ion), delay time (τ), and power dissipation (PDP) for the high-performance (HP)/low-power (LP) devices even after the gate length is lowered to 4/5 nm for n-type and 3/5 for p-type respectively. As a result, AlP is a channel candidate that could be considered for use in the next era of MOSFETs.

Sub-9 nm high-performance and low-power transistors based on an in-plane NbSe2/MoSe2/NbSe2 heterojunction.

Due to the ability to reduce the gate length of field-effect transistors (FETs) down to sub-10 nm without obviously affecting the performance of the device, the utilization of two-dimensional (2D) semiconductor materials as channel materials for FETs is of great interest. However, in-plane 2D/2D heterojunction FETs have received less attention in previous studies than vertical van der Waals heterojunction devices. Based on the above reasons, this study has investigated the transport properties of an in-plane NbSe2/MoSe2/NbSe2 heterojunction FET with different gate lengths by using ab initio quantum transport simulation. The results reveal that a gate length of sub-9 nm gives the device a low subthreshold swing down to 62 mV dec-1 and a high on-state current up to 1040 μA μm-1. Most importantly, the on-state current, delay time, and power dissipation of the FET with the optimized channel length can nearly meet or even exceed the high-performance and low-power requirements of the International Technology Roadmap for Semiconductors. The findings for this FET can provide the design and development guidance for other in-plane heterojunction electrical devices in the post-Moore era.

Dual transmission channels at metal-MoS2/WSe2 hetero-bilayer interfaces.

van der Waals heterostructures (vdWHs) open the possibility of creating novel semiconductor materials at the atomic scale that demonstrate totally new physics and enable unique functionalities, and have therefore attracted great interest in the fields of advanced electronic and optoelectronic devices. However, the interactions between metals and vdWHs semiconductors require further investigation as they directly affect or limit the advancement of high-performance electronic devices. Here we study the contact behavior of MoS2/WSe2 vdWHs in contact with a series of bulk metals using ab initio electronic structure calculations and quantum transport simulations. Our study shows that dual transmission paths for electrons and holes exist at the metal-MoS2/WSe2 hetero-bilayer interfaces. In addition, the metal-induced bandgap state (MIGS) of the original monolayer disappears due to the creation of the heterolayer, which weakens the Fermi level pinning (FLP) effect. We also find that the creation of the heterolayer causes a change in the Schottky barrier height (SBH) of the non-ohmic contact systems, whilst this does not occur so easily in the ohmic contact systems. In addition, our results indicate that when Al, Ag and Au are in contact with a MoS2/WSe2 hetero-bilayer semiconductor, a low contact barrier exists throughout the whole transmission process causing the charge to tunnel to the MoS2 layer, irrespective of whether the MoS2 is in contact with the metals as the nearest layer or as the next-nearest layer. Our work not only offers new insights into electrical contact issues between metals and hetero-bilayer semiconductors, but also provides guidance for the design of high-performance vdWHs semiconductor devices.

Performance Limit of Gate-All-Around Si Nanowire Field-Effect Transistors: An Ab Initio Quantum Transport Simulation

The gate-all-around (GAA) $\mathrm{Si}$ nanowire (NW) field-effect transistor (FET) is considered one of the most promising successors of the current mainstream $\mathrm{Si}$ fin FET (FinFET) owing to its better electrostatic gate control. Experimentally, the diameter of $\mathrm{Si}$ NWs has been scaled down to 1 nm. In this paper, the performance limit of the GAA $\mathrm{Si}$ NWFET with a 1-nm diameter is investigated by utilizing ab initio quantum transport simulations. We prove that the electrical conduction is concentrated in the core of the ultranarrow wire channel. The minimum gate length (${L}_{g}$) at which the n- and p-type GAA $\mathrm{Si}$ NWFET can satisfy the high-performance application requirements (on-state current, gate capacitance, delay time, and power dissipation) of the International Technology Roadmap for Semiconductors is 3 nm. The best-performing 5-nm-${L}_{g}$ n-type GAA $\mathrm{Si}$ NWFET exhibits an energy-delay product comparable with typical monolayer two-dimensional FETs. Compared with the similar-sized trigate $\mathrm{Si}$ NW FinFET, an approximately 200% increase in the on-state current and about 15% decrease in the subthreshold swing are witnessed in GAA $\mathrm{Si}$ NWFET at the same 5-nm ${L}_{g}$. Through strain engineering, about an 80% increase of on-state current is observed in the 5-nm-${L}_{g}$ p-type GAA $\mathrm{Si}$ NWFET. Our research demonstrates the vast potential of the GAA $\mathrm{Si}$ NWFET in the sub-3-nm gate-length region.

Ab initio quantum transport simulations of monolayer GeS nanoribbons

Monolayer germanium monosulfide (GeS) was recently identified as one of the most promising 2D materials for ultra-scaled FETs. While sub-10 nm monolayer GeS FETs were studied by quantum transport, very little is known about GeS nanoribbons (GeSNRs) or GeSNR FET performance. In this work, we employ quantum transport and Hamiltonians with an orbital resolution to study the electronic, transport, and ballistic device properties of sub-4 nm-wide and ∼15 nm-long GeSNRs. While ultra-scaled GeSNR FETs exhibit ION/IOFF of at least ∼7×105, indicating good switching performance, they also offer modest ballistic ION values of up to ∼1.2 mA/μm.