Hu Huiyong

Determination of conduction band edge characteristics of strained Si/Si1-xGex

The feature of conduction band (CB) of Tensile-Strained Si(TS-Si) on a relaxed Si1-xGex substrate is systematically investigated, including the number of equivalent CB edge energy extrema, CB energy minima, the position of the extremal point, and effective mass. Based on an analysis of symmetry under strain, the number of equivalent CB edge energy extrema is presented; Using the KP method with the help of perturbation theory, dispersion relation near minima of CB bottom energy, derived from the linear deformation potential theory, is determined, from which the parameters, namely, the position of the extremal point, and the longitudinal and transverse masses (m*1 and m*t) are obtained.

Two-dimensional threshold voltage model of a nanoscale silicon-on-insulator tunneling field-effect transistor

The tunneling field-effect transistor (TFET) is a potential candidate for the post-CMOS era. In this paper, a threshold voltage model is developed for this new kind of device. First, two-dimensional (2D) models are used to describe the distributions of potential and electric field in the channel and two depletion regions. Then based on the physical definition of threshold voltage for the nanoscale TFET, the threshold voltage model is developed. The accuracy of the proposed model is verified by comparing the calculated results with the 2D device simulation data. It has been demonstrated that the effects of varying the device parameters can easily be investigated using the model presented in this paper. This threshold voltage model provides a valuable reference to TFET device design, simulation, and fabrication.

Early effect modeling of silicon-on-insulator SiGe heterojunction bipolar transistors

Silicon germanium (SiGe) heterojunction bipolar transistor (HBT) on thin silicon-on-insulator (SOI) has recently been demonstrated and integrated into the latest SOI BiCMOS technology. The Early effect of the SOI SiGe HBT is analysed considering vertical and horizontal collector depletion, which is different from that of a bulk counterpart. A new compact formula of the Early voltage is presented and validated by an ISE TCAD simulation. The Early voltage shows a kink with the increase of the reverse base—collector bias. Large differences are observed between SOI devices and their bulk counterparts. The presented Early effect model can be employed for a fast evaluation of the Early voltage and is useful to the design, the simulation and the fabrication of high performance SOI SiGe devices and circuits.

Novel vertical stack HCMOSFET with strained SiGe/Si quantum channel

A novel vertical stack heterostructure CMOSFET is investigated, which is structured by strained SiGe/Si with a hole quantum well channel in the compressively strained Si1?xGex layer for p-MOSFET and an electron quantum well channel in the tensile strained Si layer for n-MOSFET. The device possesses several advantages including: 1) the integration of electron quantum well channel with hole quantum well channel into the same vertical layer structure; 2) the gate work function modifiability due to the introduction of poly-SiGe as a gate material; 3) better transistor matching; and 4) flexibility of layout design of CMOSFET by adopting exactly the same material lays for both n-channel and p-channel. The MEDICI simulation result shows that p-MOSFET and n-MOSFET have approximately the same matching threshold voltages. Nice performances are displayed in transfer characteristic, transconductance and cut-off frequency. In addition, its operation as an inverter confirms the CMOSFET structured device to be normal and effective in function.

Enhanced electroluminescence from a free-standing tensilely strained germanium nanomembrane light-emitting diode

Ge has become a promising material for Si-based optoelectronic integrated circuits (OEIC) due to its pseudo-direct bandgap.In this paper we achieved tensilely strained Ge free-standing nanomembrane (NM) lightemitting diode (LED), using silicon nitride thin film with high stress.The tensile stress in the Ge layer can be controlled by adjustable process parameters.An expected redshift of electroluminescence (EL) in Ge NM LED is observed at room temperature, which has been attributed to the shrinking of its direct bandgap relative to its indirect bandgap.An EL with dramatically increased intensity was observed around 1876 nm at a tensile strain of 1.92%, which demonstrates the direct-band recombination in tensilely strained Ge NM.

Analytical base-collector depletion capacitance in vertical SiGe heterojunction bipolar transistors fabricated on CMOS-compatible silicon on insulator

The base—collector depletion capacitance for vertical SiGe npn heterojunction bipolar transistors (HBTs) on silicon on insulator (SOI) is split into vertical and lateral parts. This paper proposes a novel analytical depletion capacitance model of this structure for the first time. A large discrepancy is predicted when the present model is compared with the conventional depletion model, and it is shown that the capacitance decreases with the increase of the reverse collector—base bias—and shows a kink as the reverse collector—base bias reaches the effective vertical punch-through voltage while the voltage differs with the collector doping concentrations, which is consistent with measurement results. The model can be employed for a fast evaluation of the depletion capacitance of an SOI SiGe HBT and has useful applications on the design and simulation of high performance SiGe circuits and devices.

Calculation of band edge levels of strained Si/(111)Si1–xGex

Calculations were performed on the band edge levels of (111)-biaxially strained Si on relaxed Si1–xGex alloy using the k · p perturbation method coupled with deformation potential theory. The results show that the conduction band (CB) edge is characterized by six identical valleys, that the valence band (VB) edge degeneracies are partially lifted, and that both the CB and VB edge levels move up in electron energy as the Ge fraction (x) increases. In addition, the dependence of the indirect bandgap and the VB edge splitting energy on x was obtained. Quantitative data from the results supply valuable references for Si-based strained device design.

Structural feature and electronic property of an (8, 0) carbon--silicon carbide nanotube heterojunction

A supercell of a nanotube heterojunction formed by an (8, 0) carbon nanotube (CNT) and an (8, 0) silicon carbide nanotube (SiCNT) is established, in which 96 C atoms and 32 Si atoms are included. The geometry optimization and the electronic property of the heterojunction are implemented through the first-principles calculation based on the density functional theory (DFT). The results indicate that the structural rearrangement takes place mainly on the interface and the energy gap of the heterojunction is 0.31 eV, which is narrower than those of the isolated CNT and the isolated SiCNT. By using the average bond energy method, the valence band offset and the conduction band offset are obtained as 0.71 and −0.03 eV, respectively.

Averaged hole mobility model of biaxially strained Si

We aim to establish a model of the averaged hole mobility of strained Si grown on (001), (101), and (111) relaxed Si1?x Gex substrates. The results obtained from our calculation show that their hole mobility values corresponding to strained Si (001), (101) and (111) increase by at most about three, two and one times, respectively, in comparison with the unstrained Si. The results can provide a valuable reference to the understanding and design of strained Si-based device physics.

The effect of substrate doping on the flatband and threshold voltages of a strained-Si pMOSFET

The effect of substrate doping on the flatband and threshold voltages of a strained-Si/SiGe p metal—oxide semiconductor field-effect transistor (pMOSFET) has been studied. By physically deriving the models of the flatband and threshold voltages, which have been validated by numerical simulation and experimental data, the shift in the plateau from the inversion region to the accumulation region as the substrate doping increases has been explained. The proposed model can provide a valuable reference to the designers of strained-Si devices and has been implemented in software for extracting the parameters of a strained-Si MOSFET.