DEVELOPER COMMUNITY

In the following we will show an advanced application of tiberCAD which involves atomistic calculations based on the Empirical Tight Binding (ETB) approach.

This feature is not yet implemented in the current version 2.0, but it will be available from the next tiberCAD release.

Here we present 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.

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, 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 the last couple of years a huge effort has been devoted to achieve and to control the growth of III-nitride columnar-shaped nanostructures: nanorods, nanocolumns, nanopillars. Results have shown, so far, an extremely high crystal quality of the AlGaN nanocolumns, that are strain-free and have no dislocations or other extended defects, thus, yielding an outstanding emission efficiency. The achievement of nanocolumnar heterostructures including quantum disks (QDisks) and nanocavities with QDisks and Bragg mirrors have been reported.