Lasing is experimentally demonstrated in a direct bandgap GeSn alloy, grown directly onto Si(001). The authors observe a clear lasing threshold as well as linewidth narrowing at low temperatures.

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Lasing in direct-bandgap GeSn alloy grown on Si

Progress in the development of tunnel field-effect transistors (TFETs) is reviewed by comparing experimental results and theoretical predictions against 16-nm FinFET CMOS technology. Experiments lag the projections, but sub-threshold swings less than 60 mV/decade are now reported in 14 TFETs. The lowest measured sub-threshold swings approaches 20 mV/decade, however, the measurements at these lowest values are not based on many points. The highest current at which sub-threshold swing below 60 mV/decade is observed is in the range 1–10 nA/ ${{\mu }}$ m. A common approach to TFET characterization is proposed to facilitate future comparisons.

Tunnel Field-Effect Transistors: State-of-the-Art

Two-dimensional (2D) crystal semiconductors, such as the well-known molybdenum disulfide (MoS2), are witnessing an explosion in research activities due to their apparent potential for various electronic and optoelectronic applications. In this paper, dissipative quantum transport simulations using nonequilibrium Green’s function formalism are performed to rigorously evaluate the scalability and performance of monolayer/multilayer 2D semiconductor-based FETs for sub-10 nm gate length very large-scale integration (VLSI) technologies. Device design considerations in terms of the choice of prospective 2D material/structure/technology to fulfill sub-10 nm International Technology Roadmap for Semiconductors (ITRS) requirements are analyzed. First, it is found that MoS2 FETs can meet high-performance (HP) requirement up to 6.6 nm gate length using bilayer MoS2 as the channel material, while low-standby-power (LSTP) requirements present significant challenges for all sub-10 nm gate lengths. Second, by studying the effects of underlap (UL) structures, scattering strength, and carrier effective mass, it is found that the high mobility and suitably low effective mass of tungsten diselenide (WSe2), aided by the UL, enable 2D FETs for both HP and LSTP applications at the smallest foreseeable (5.9 nm) gate length. Finally, possible solutions for sub-5 nm gate lengths, specifically anisotropic 2D semiconductor materials for HP and sub- $kT/q$ switch (2D tunnel FET) for LSTP, are also proposed based on the effects of critical material parameters on the device performance.

2D Semiconductor FETs—Projections and Design for Sub-10 nm VLSI

Si–Ge–Sn alloys: From growth to applications

Low-dimensional semiconductor materials structures, where nanowires are needle-like one-dimensional examples, have developed into one of the most intensely studied fields of science and technology. The subarea described in this review is compound semiconductor nanowires, with the materials covered limited to III-V materials (like GaAs, InAs, GaP, InP,...) and III-nitride materials (GaN, InGaN, AlGaN,...). We review the way in which several innovative synthesis methods constitute the basis for the realization of highly controlled nanowires, and we combine this perspective with one of how the different families of nanowires can contribute to applications. One reason for the very intense research in this field is motivated by what they can offer to main-stream semiconductors, by which ultrahigh performing electronic (e.g., transistors) and photonic (e.g., photovoltaics, photodetectors or LEDs) technologies can be merged with silicon and CMOS. Other important aspects, also covered in the review, deals with synthesis methods that can lead to dramatic reduction of cost of fabrication and opportunities for up-scaling to mass production methods.

Synthesis and Applications of III-V Nanowires

This work investigates the electronic band structures of bulk Ge1-xSnx alloys using the empirical pseudopotential method (EPM) for Sn composition x varying from 0 to 0.2. The adjustable form factors of EPM were tuned in order to reproduce the band features that agree well with the reported experimental data. Based on the adjusted pseudopotential form factors, the band structures of Ge1-xSnx alloys were calculated along high symmetry lines in the Brillouin zone. The effective masses at the band edges were extracted by using a parabolic line fit. The bowing parameters of hole and electron effective masses were then derived by fitting the effective mass at different Sn compositions by a quadratic polynomial. The hole and electron effective mass were examined for bulk Ge1-xSnx alloys along specific directions or orientations on various crystal planes. In addition, employing the effective-mass Hamiltonian for diamond semiconductor, band edge dispersion at the Γ-point calculated by 8-band k.p. method was fitted...

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Electronic band structure and effective mass parameters of Ge1-xSnx alloys

Tunneling field-effect transistor (TFET) could achieve sub-60 mV/decade subthreshold swing S at room temperature and could enable ultra-low supply voltage V DD and power consumption. Drive current above 100 μA/μm was achieved in III-V-based n-channel TFETs (nTFETs), due to the direct BTBT and high electron mobility in III-V materials [1–2]. However, more research is needed for p-channel TFET (pTFET). While III-V materials have high direct band-to-band tunneling (BTBT) rate, hole mobilities are generally low and lead to high channel resistance [Fig. 1(b)]. SiGe or Ge have high hole mobility and might be promising for pTFETs, but the the BTBT is indirect and the on-state current is low. Also, high activation temperature and large diffusivity of n-type dopants in Ge make it very difficult to form good N+/P junction in Ge.

Towards direct band-to-band tunneling in P-channel tunneling field effect transistor (TFET): Technology enablement by Germanium-tin (GeSn)

We report the demonstration of germanium-tin (GeSn) p-channel tunneling field-effect transistor (p-TFET) with good device performance in terms of on-state current (Ion). With the incorporation of Sn, the conduction band minima at Γ-point of GeSn alloy shift down, increasing the direct band-to-band tunneling (BTBT) generation rate at the source-channel tunneling junction in TFET. In addition, n-type dopant activation temperature of below 400 °C can be used in GeSn, which is much lower than that in Ge (700 °C). Therefore, n-type dopant diffusion in GeSn is suppressed leading to an abrupt n+ tunneling junction that is favorable for the source junction of a p-TFET. Lateral Ge0.958Sn0.042 p-TFETs were fabricated and high Ion of 29 μA/μm at VGS = VDS = -2 V and 4.34 μA/μm at VGS = VDS = -1 V is achieved.

Germanium–Tin P-Channel Tunneling Field-Effect Transistor: Device Design and Technology Demonstration

The ballistic transport performance of field-effect transistor (FET) based on hydrogenated silicene and germanene, i.e., silicane and germanane, respectively, is examined. The electronic band structures of silicane and germanane are investigated using the first-principles density functional theory. Subsequently, the ballistic performance of FETs is evaluated via the semiclassical ballistic transport model. We find that silicane n-MOSFET offers a relatively better ON-current performance than transistors made of germanane and 2-D transition metal dichalcogenides (2-D-TMDs) (MoS2, MoSe2, WS2, and WSe2). Germanane n-MOSFET suffers from the issue of low density of states due to its smaller electron effective mass. P-FETs based on germanane and silicane have higher ON-current than those of 2-D-TMDs p-FETs. Further investigation on other aspects of silicane and germanane MOSFETs, such as gate leakage and contact resistance, is needed to comprehensively assess their overall performance metrics.

Ballistic Transport Performance of Silicane and Germanane Transistors

We investigate germanium-tin alloy (Ge1−xSnx) as a material for the design of tunneling field-effect transistor (TFET) operating at low supply voltages. Compared with Ge, Ge1−xSnx has a smaller band-gap. The reported band-gap of Ge0.89Sn0.11 is 0.477 eV, ∼28% smaller than that of Ge. More importantly, Ge1−xSnx becomes a direct band-gap material when Sn composition x is higher than 0.11. By employing Ge1−xSnx in TFET, direct band-to-band tunneling (BTBT) is realized. Direct BTBT generally has higher tunneling probability than indirect BTBT. The drive current of TFET is boosted due to the direct BTBT and the reduced band-gap of Ge1−xSnx. Device simulations show that the drive current and subthreshold swing S characteristics of Ge1−xSnx TFETs with x ranging from 0 to 0.2 are improved by increasing the Sn composition x. For Ge0.8Sn0.2 TFET, sub-60 mV/decade S is achieved at a high current level of ∼8 μA/μm. For x higher than 0.11, Ge1−xSnx TFETs show higher on-state current ION compared to Ge TFET at a supply...

Kain Lu Low

Papers

Electronic band structure and effective mass parameters of Ge1-xSnx alloys

Towards direct band-to-band tunneling in P-channel tunneling field effect transistor (TFET): Technology enablement by Germanium-tin (GeSn)

Germanium–Tin P-Channel Tunneling Field-Effect Transistor: Device Design and Technology Demonstration

Ballistic Transport Performance of Silicane and Germanane Transistors

Germanium-tin n-channel tunneling field-effect transistor: Device physics and simulation study