DEVELOPER COMMUNITY

In this application, we show the results of fully Self-Consistent Schroedinger (EFA) - Drift-diffusion calculations for a 3D nanostructure: an AlGaAs rectangular nanocolumn p-i-n diode structure with an embedded GaAs quantum well.

Here is an overview of the approach chosen for self-consistent calculation in tiberCAD.

First, the solution of the eigenvalue problems resulting from the quantum EFA model provides the energy spectrum and the particle densities. The particle densities are calculated by populating the electron and hole states according to the expectation value of the corresponding electrochemical potential; then they are fed back to the Poisson/drift-diffusion model for self-consistent Schroedinger–Poisson/drift-diffusion calculations. These can be classified as overlap type simulations, where the results of the nanoscale calculation acts as an input – e.g. in form of parameters – to the microscale simulation.

In this application, a full 3D model of an AlGaN nanocolumn heterostructure with a GaN quantum disk has been designed and used to perform 3D quantum calculations and obtain eigenvalues and eigenfunctions of confined states in the quantum disk (QD).

We first perform a strain simulation, to get deformation potentials and piezopolarization, than we apply drift-diffusion model with an increasing bias to the contacts, until the nanocolumn diode is brought in conduction regime. Then quantum efa calculations are performed to get the electron and hole states in the QD. Then, from these states in conduction and valence band, the optical emission spectrum is calculated. Finally, the quantum density for electrons and holes in the QD is calculated and compared to classical densities.

In this application, we show a 1D calculation of quantum and optical properties of a AlGaN/GaN LED diode with three GaN quantum wells.

The simulated structure is the following:
After a buffer n-doped AlGaN layer, a Al_0.78InN barrier layer is present, then a series of three AlGaN/GaN quantum wells, each 2 nm-wide, followed by a p-doped AlGaN layer.

In this wurtzite nitride heterostructure, strain and strain induced piezoelectric polarization play a fundamental role in the description of the electronic properties. In fact, on one hand, effects of strain on the conduction and band profiles have to be taken in account through the appropriate k.p model and, on the other hand, the piezoelectric polarization term, together with the spontaneous polarization one, have  to be included in the Poisson-Drift-Diffusion calculations.

In this application, we have applied TiberCAD to 3D calculations of electrical characteristics of a Si-based 3-gate Finfet device.

For the last years, three-dimensional Multi-gate FET devices (double , triple or quadruple-gate) have been evolving from the silicon-on-insulator (SOI) classical, planar single gate MOSFET, in order to satisfy increasing need for higher current drive and better short channel behaviour.

The first fully depleted SOI MOSFET (early 1980's) showed superior transconductance, current drive and subthreshold swing. Its development led to the double-gate SOI MOSFET, which provided good short-channel characteristics due to the better gate control on the channel. A natural evolution of the latter was the vertical-channel double-gate FinFET. Triple-gate and gate-all-around implementations of the FinFET structure followed shortly. The phenomenon of volume inversion, leading to large transconductance, has encouraged the development of a series of these structures, ranging from quantum-wire MOSFET to circular section surrounding-gate devices with a pillar-like silicon island and vertical channel.

We consider here a three-gate FinFET structure with a 20 nm thick and 40 nm high Silicon fin. The channel length is 50 nm and the gate oxide thickness is 2 nm; we will see in the following the effects of the scaling of the device.

TiberCAD allows a multiscale simulation approach to simulation of MOSFET devices. This kind of simulation includes both macroscopic drift-diffusion current model and quantum tunneling model. The models are solved together in a self-consistent way. As an example, we study the subthreshold transfer characteristics of MOSFETs based on high-k oxides. We compare the high-k gates based on HfO₂ and ZrO₂ with a SiO₂ gate of the same equivalent thickness and show the effect of the gate oxide tunneling current on transistor performance.