In this paper, a dopingless fin-shaped SiGe channel TFET (DF-TFET) is proposed and studied. To form a high-efficiency dopingless line tunneling junction, a fin-shaped SiGe channel and a gate/source overlap are induced. Through these methods, the DF-TFET with high on-state current, switching ratio of 12 orders of magnitude and no obvious ambipolar effect can be obtained. High κ material stack gate dielectric is induced to improve the off-state leakage, interface characteristics and the reliability of DF-TFET. Moreover, by using the dopingless channel and fin structure, the difficulties of doping process and asymmetric gate overlap formation can be resolved. As a result, the structure of DF-TFET can possess good manufacture applicability and remarkably reduce footprint. The physical mechanism of device and the effect of parameters on performance are studied in this work. Finally, on-state current (I_ON) of 58.8 μA/μm, minimum subthreshold swing of 2.8 mV/dec (SS_min), average subthreshold swing (SS_avg) of 18.2 mV/dec can be obtained. With improved capacitance characteristics, cutoff frequency of 5.04 GHz and gain bandwidth product of 1.29 GHz can be obtained. With improved performance and robustness, DF-TFET can be a very attractive candidate for ultra-low-power applications.

As an important supplementary material to graphene in the optoelectronics field, molybdenum disulfide (MoS₂) has attracted attention from researchers due to its good light absorption capacity and adjustable bandgap. In this paper, MoS₂ layers are respectively grown on SiO₂/Si and sapphire substrates by atmospheric pressure chemical vapor deposition (APCVD). Atomic force microscopy, optical microscopy, and Raman and photoluminescence spectroscopy are used to probe the optical properties of MoS₂ on SiO₂/Si and sapphire substrates systematically. The peak shift between the characteristic A_1g and E¹_2g peaks increases, and the I peak of the PL spectrum on the SiO₂/Si substrate redshifts slightly when the layer numbers were increased, which can help in obtaining the layer number and peak position of MoS₂. Moreover, the difference from monolayer MoS₂ on the SiO₂/Si substrate is that the B peak of the PL spectrum has a blueshift of 56 meV and the characteristic E¹_2g peak of the Raman spectrum has no blueshift. The 1- and 2-layer MoS₂ on a sapphire substrate had a higher PL peak intensity than that of the SiO₂/Si substrate. When the laser wavelength is transformed from 532 to 633 nm, the position of I exciton peak has a blueshift of 16 meV, and the PL intensity of monolayer MoS₂ on the SiO₂/Si substrate increases. The optical properties of MoS₂ can be obtained, which is helpful for the fabrication of optoelectronic devices.

In this paper, a dual metallic material gate heterostructure junctionless tunnel field-effect transistor (DMMG-HJLTFET) is proposed and investigated. We use the Si/SiGe heterostructure at the source/channel interface to improve the band to band tunneling (BTBT) rate, and introduce a sandwich stack (GaAs/Si/GaAs) at the drain region to suppress the OFF-state current and ambiplolar current. Simultaneously, to further decrease ambipolar current, the gate electrode is divided into three parts namely auxiliary gate (M1), control gate (M2), and tunnel gate (M3) with workfunctions Φ_M1, Φ_M2 and Φ_M3, respectively, where Φ_M1 = Φ_M3 < Φ_M2. Simulation results indicate that DMMG-HJLTFET provides superior performance in terms of logic and analog/RF as compared with other possible combinations, the ON-state current of the DMMG-HJLTFET increases up to $9.04\times 10^{-6}$ A/μm, and the maximum g_m (which determine the analog performance of devices) of DMMG-HJLTFET is $1.11\times 10^{-5}$ S/μm at 1.0V drain-to-source voltage (Vds). Meanwhile, RF performance of devices depends on the cut-off frequency (f_T) and gain bandwidth (GBW), and DMMG-HJLTFET could achieve a maximum f_T of 5.84 GHz, and a maximum GBW of 0.39 GHz, respectively.

The general preparation method of large-area, continuous, uniform, and controllable vdW heterostructure materials is provided in this paper. To obtain the preparation of MoS₂/h-BN and WS₂/h-BN heterostructures, MoS₂ and WS₂ material are directly grown on the insulating h-BN substrate by atmospheric pressure chemical vapor deposition (APCVD) method, which does not require any intermediate transfer steps. The test characterization of MoS₂/h-BN and WS₂/h-BN vdW heterostructure materials can be accomplished by optical microscope, AFM, Raman and PL spectroscopy. The Raman peak signal of h-BN material is stronger when the h-BN film is thicker. Compared to the spectrum of MoS₂ or WS₂ material on SiO₂/Si substrate, the Raman and PL spectrum peak positions of MoS₂/h-BN heterostructure are blue-shifted, which is due to the presence of local strain, charged impurities and the vdW heterostructure interaction. Additionally, the PL spectrum of WS₂ material shows the strong emission peak at 1.96 eV, while the full width half maximum (FWHM) is only 56 meV. The sharp emission peak indicates that WS₂/h-BN heterostructure material has the high crystallinity and clean interface. In addition, the peak position and shape of IPM mode characteristic peak are not obvious, which can be explained by the Van der Waals interaction of WS₂/h-BN heterostructure. From the above experimental results, the preparation method of heterostructure material is efficient and scalable, which can provide the important support for the subsequent application of TMDs/h-BN heterostructure in nanoelectronics and optoelectronics.

To improve the on-state current and reduce the miller capacitance of the conventional junction-less tunneling field effect transistor (JLTFET), the junction-less TFET with Ge/Si_0.3Ge_0.7/Si heterojunction and heterogeneous gate dielectric (H-JLTFET) is investigated by the Technology Computer Aided Design (TCAD) simulation in this paper. The source region uses the narrow bandgap semiconductor material germanium to obtain the higher on-state current; the gate dielectric adjacent to the drain region adopts the low-k dielectric material SiO₂, which is considered to reduce the gate-to-drain capacitance effectively. Moreover, the gap region uses the Si_0.3Ge_0.7 material to decrease the tunneling distance. In addition, the effects of the device sizes, doping concentration and work function on the performance of the H-JLTFET are analyzed systematically. The optimal on-state current and switching ratio of the H-JLTFET can reach 6 µA/µm and 2.6 × 10¹², which are one order of magnitude and four orders of magnitude larger than the conventional JLTFET, respectively. Meanwhile, the gate-to-drain capacitance, off-state current and power consumption of the H-JLTFET can be effectively suppressed, so it will have a great potential in future ultra-low power integrated circuit applications.

The Van der Waals (vdWs) hetero-structures consist of two-dimensional materials have received extensive attention, which is due to its attractive electrical and optoelectronic properties. In this paper, the high-quality large-size graphene film was first prepared by the chemical vapor deposition (CVD) method; then, graphene film was transferred to SiO₂/Si substrate; next, the graphene/WS₂ and graphene/MoS₂ hetero-structures were prepared by the atmospheric pressure chemical vapor deposition method, which can be achieved by directly growing WS₂ and MoS₂ material on graphene/SiO₂/Si substrate. Finally, the test characterization of graphene/TMDs hetero-structures was performed by AFM, SEM, EDX, Raman and PL spectroscopy to obtain and grasp the morphology and luminescence laws. The test results show that graphene/TMDs vdWs hetero-structures have the very excellent film quality and spectral characteristics. There is the built-in electric field at the interface of graphene/TMDs heterojunction, which can lead to the effective separation of photo-generated electron–hole pairs. Monolayer WS₂ and MoS₂ material have the strong broadband absorption capabilities, the photo-generated electrons from WS₂ can transfer to the underlying p-type graphene when graphene/WS₂ hetero-structures material is exposed to the light, and the remaining holes can induced the light gate effect, which is contrast to the ordinary semiconductor photoconductors. The research on spectral characteristics of graphene/TMDs hetero-structures can pave the way for the application of novel optoelectronic devices.