Enrique G. Marin

Analytical Gate Capacitance Modeling of III–V Nanowire Transistors

In this paper, we propose a physically based analytical model for the gate capacitance (CG) of III-V nanowire (NW) transistors. The model explicitly accounts for different terms that contribute to CG: the insulator capacitance, the finite density of states, and the charge distribution in the NW. It considers the 2-D quantum confinement of the carriers, the wavefunction penetration into the gate insulator, Fermi-Dirac statistics and the conduction band nonparabolicity, providing analytical expressions for all the capacitance contributions. Furthermore, the behavior and role of the density of states and the charge distribution in the NW are discussed for several materials and the influence of the wavefunction penetration into the gate insulator is also studied. We show that our analytical model is in very good agreement with the numerical solution for different device sizes and materials.

Analytic potential and charge model for III-V surrounding gate metal-oxide-semiconductor field-effect transistors

In this work, an analytical model is proposed to calculate the potential and the inversion charge of III-V cylindrical Surrounding-Gate metal-oxide-semiconductor field-effect transistors (MOSFETs). The model provides expressions for the calculation of the subband energies and their corresponding wavefunctions, taking into account their penetration into the gate insulator and the effective mass discontinuity in the semiconductor-insulator interface for this kind of devices. The model considers Fermi-Dirac statistics and the two-dimensional quantum confinement of the carriers. We demonstrate that our analytical solution fits very well the numerical solution in all operating regimes and for different device sizes and materials.

Theoretical interpretation of the electron mobility behavior in InAs nanowires

This work studies the electron mobility in InAs nanowires (NWs), by solving the Boltzmann Transport Equation under the Momentum Relaxation Time approximation. The numerical solver takes into account the contribution of the main scattering mechanisms present in III-V compound semiconductors. It is validated against experimental field effect-mobility results, showing a very good agreement. The mobility dependence on the nanowire diameter and carrier density is analyzed. It is found that surface roughness and polar optical phonons are the scattering mechanisms that mainly limit the mobility behavior. Finally, we explain the origin of the oscillations observed in the mobility of small NWs at high electric fields.

Mobility and Capacitance Comparison in Scaled InGaAs Versus Si Trigate MOSFETs

In this letter, we study the electronic properties of InGaAs and Si trigates using the nonparabolic effective mass approximation and up-to-date mobility models. Our comprehensive simulations estimate a strong reduction of the InGaAs electron mobility to values even lower than those achieved with Si. Considering the reduction of the gate capacitance due to the low density-of-states of the III-V alloy, no apparent benefit would be obtained from using InGaAs trigates instead of Si ones unless high quality interfaces can be achieved. We conclude that the potential application of InGaAs trigates as a reference device for future technological nodes is seriously jeopardized by the quality of the semiconductor-insulator interface.

Impact of the Back-Gate Biasing on Trigate MOSFET Electron Mobility

In this brief, the influence of the back-gate biasing, Vbg, on the electron mobility of Si trigates on ultrathin buried oxide is studied, using state of the art scattering models for 2-D confined devices. The variation of the back-gate influence with the device size is analyzed and explained addressing to the charge redistribution in the channel. The lower confinement of larger devices results in strong changes in the electron mobility as Vbg is modified, contrary to what is observed in smaller devices. The charge redistribution due to Vbg also affects the relative influence of the interface walls, which is analyzed in depth. The impact on the mobility of the main scattering mechanisms as a function of Vbg is also discussed.

The unexpected beneficial effect of the L-valley population on the electron mobility of GaAs nanowires

The impact of the L-valley population on the transport properties of GaAs cylindrical nanowires (NWs) is analyzed by numerically calculating the electron mobility under the momentum relaxation time approximation. In spite of its low contribution to the electron mobility (even for high electron populations in small NWs), it is demonstrated to have a beneficial effect, since it significantly favours the Γ-valley mobility by screening the higher Γ-valley energy subbands.

Electrostatic performance of InSb, GaSb, Si and Ge p-channel nanowires

The electrostatic performance of p-type nanowires (NWs) made of InSb and GaSb, with special focus on their gate capacitance behavior, is analyzed and compared to that achieved by traditional semiconductors usually employed for p-MOS such as Si and Ge. To do so, a self-consistent kp simulator has been implemented to achieve an accurate description of the Valence Band and evaluate the charge behavior as a function of the applied gate bias. The contribution and role of the constituent capacitances, namely the insulator, centroid and quantum ones are assessed. It is demonstrated that the centroid and quantum capacitances are strongly dependent on the semiconductor material. We find a good inherent electrostatic performance of GaSb and InSb NWs, comparable to their Ge and Si counterparts making these III-Sb compounds good candidates for future technological nodes.

Implicit versus explicit momentum relaxation time solution for semiconductor nanowires

We discuss the necessity of the exact implicit Momentum Relaxation Time (MRT) solution of the Boltzmann transport equation in order to achieve reliable carrier mobility results in semiconductor nanowires. Firstly, the implicit solution for a 1D electron gas with a isotropic bandstructure is presented resulting in the formulation of a simple matrix system. Using this solution as a reference, the explicit approach is demonstrated to be inaccurate for the calculation of inelastic anisotropic mechanisms such as polar optical phonons, characteristic of III-V materials. Its validity for elastic and isotropic mechanisms is also evaluated. Finally, the implications of the MRT explicit approach inaccuracies on the total mobility of Si and III-V NWs are studied.

Influence of alloy disorder scattering on the hole mobility of SiGe nanowires

In this work, we analyze the influence of the alloy disorder (AD) scattering on the low-field hole mobility of Si1-xGex nanowires (NWs). To do it, the electrostatic description is achieved through a self-consistent solution of the Poisson equation and the six-band k⋅p method in the cross section of the NW. The momentum relaxation time approximation is used to calculate the hole mobility, including alloy disorder and phonon scattering mechanisms, and the use of approximations to calculate the overlap integrals for the scattering matrix elements is discussed. We study the influence of the alloy disorder scattering on the total mobility compared to the phonon contribution, for different values of the AD scattering parameter proposed in the literature, and analyze the performance of SiGe NWs as a function of the Ge molar fraction for both low and high inversion charge densities.

On the influence of the back-gate bias on InGaAs Trigate MOSFETs

We analyze the behavior of InGaAs Trigate MOSFETs under the influence of a back-gate bias, Vbg. The charge distribution, the body-factor, the threshold voltage and the electron mobility dependences on Vbg are discussed. The InGaAs devices are benchmarked against Si ones demonstrating a higher impact of the back-gate bias for the formers, causing larger body factors and stronger mobility variations.