Dye Solar Cells are interesting third generation photovoltaic devices. A DSC is fundamentally an electrochemical device where a molecule chemisorbed onto the surface of a porous material absorbs light and transfer an electron to the substrate. The ionized molecule is regenerated by the electrolyte which permeates the cell. In this sense the DSC is a majority carriers solar cell. This allows to use materials with a large amount of defects achieving in the meantime high efficiencies beyond 10%.

The DSC-Dye Solar Cell module of tiberCAD allows the simulation of a complete model of the full cell, including all the different parts of the device: the porous material, the photoactive dye, the electrolyte surrounding the semiconductor and the two contacts. The transport equations, including photogeneration and recombination, are solved using finite elements on a grid. Due to the flexibility of finite element implementation these equations can be solved on a general domain in 1, 2 and 3D.

The Drift-Diffusion module can be used for the simulation of light emitting devices, bipolar transistors, MOS transistors, HEMTs and nanostructured devices. It is particularly suited for the study of strained III-V nanostructures due to the possibility to include the full strain tensor from realistic strain maps and quantization effects selfconsistently. The consistent treatment of inhomogeneous strain and polarization fields allows the simulation of piezoelectric devices.

The Drift-Diffusion module calculates transport of electrons and holes based on the Drift Diffusion approximation in 1, 2 and 3 dimensions. The continuity equations for electrons and holes are solved selfconsistently with the Poisson equation. The carrier densities are calculated assuming a local thermal equilibrium, using Boltzmann or Fermi-Dirac statistics. Mechanical, thermal and quantization effects can be included fully selfconsistently by coupling to the Elasticity, Thermal and Envelope Function Approximation modules.

Electromechanical modeling is becoming an essential tool to model modern devices particularly when the strain engineering is used to tune the electrical and optical properties of materials. Furthermore, an emergent class of devices, such as piezoelectric nanogenerators, are designed to convert the elastic energy into electricity. Elasticity brings features developed for continuous elasticity into device modeling. The coupled treatment of the electro-mechanical problem within a unique framework allows to explore the feasibility of devices where the mechanical deformation plays a fundamental role. Elasticity includes isotropic as well as anisotropic stiffness tensor to model the elastic properties of materials.

One of the main features of Elasticity is the possibility to calculate the strain induced by the lattice mismatch.
Once the strain map is computed, Drift-Diffusion may compute the electronic band bending due to the piezoelectric field and its effect on the electrical properties. This treatment is essential in those cases where the strain engineering plays a fundamental role such as in High Electrical Mobility Transistors (HEMTs).

The downscaling of modern devices is increasing the power density to be dissipated via thermal conducting and, in some cases, self-heating effects may degrade the device performance. There is, therefore, the need to properly model heating and dissipation due to the Joule’s effect. Thanks to its deep connection with Drift-Diffusion, Thermal has established itself as a powerful and flexible tool to compute power balance in realistic devices. Effects going beyond the standard diffusive model, such as the energy relaxation of hot electrons, can be added by a constant value heat source. Furthermore, a number of thermal boundary conditions allows to model the environment around the device in a realistic way. For example, the heat dissipated by the substrate can be modeled as an effective thermal surface resistance. Thermal insulating and conducting surfaces can be easily added, as well.

Nanostructured devices exploiting quantum mechanical effects for their functioning e.g. transistors based on quantum wires, quantum dots or molecules, are on the cutting edge of nanotechnology. To model the electronic and optical behavior of the active regions of such devices a fully quantum mechanical treatment is required. The Envelope Function Approximation (EFA) allows a rigorous quantum description of semiconductor heterostructures.
Examples of applications are: full 3D calculation of quantum states in a GaN-based nanocolumn quantum disk, optical properties of AlGaN/GaN LED diode, InGaAs/GaAs quantum wires.

Atomistic is a set of tools for the simulation of nanostructures based on atomistic approaches. It contains a Module for structure relaxation of atomic structures based on Valence Force Field (Module vff) and a Module for Empirical Tight Binding calculations (Module empirical_tb). More Modules for atomistic based simulations, such as Density-Functional TB (DFTB) and Non-Equilibrium Green Function (NEGF) for quantum transport, are scheduled for the next releases of tiberCAD. All of these Modules take advantage of a tool developed in tiberCAD for the building and handling of atomistic representations of nanostructures. This built-in Atomistic Generator allows to generate an atomic basis associated with the finite element mesh which belongs to a given physical region, based on the material specifications and the growth directions defined for that region. It supports any crystal structure with fcc, bcc, cubic and hexagonal Bravais lattice and performs hydrogen passivation for any crystal structure supported. Important features of the Atomistic generator are the possibility to apply periodicity to any direction and to import an external atomic structure file in a common format. Random alloy structures can be generated.

The Empirical Tight Binding (ETB) module allows for atomistic-based calculations of electronic and optical properties of Nanowires, Quantum Dots and Quantum Wells. Eigenstates, eigenfunctions and quantum density of a given system can be obtained by solving a tight-binding Hamiltonian by means of the Module empirical_tb. The optical properties are calculated by the Module opticstb. A nearest neighbour tight-binding model is implemented, which supports accurate sp3s*d5 parameterizations for several materials, including GaN/AlGaN/InGaN systems. Combined with the built-in Atomistic Generator and the Module vff for structure relaxation based on Valence Force Field (VFF), ETB Module allows to treat in a fundamental way nanometric features in Quantum Well and Quantum Dot active regions, such as alloy fluctuations. In fact, thanks to the flexibility of the atomistic generator, both Virtual Crystal Approximation (VCA) and random alloy approach may be used to model active regions of electronic and optoelectronic devices. Random alloy representations may provide a realistic picture of a nanostructured LED active region.

Main features:

• Built-in Atomistic Generator for any crystal structure with fcc, bcc, cubic and hexagonal Bravais lattice; implements hydrogen passivation
• Atomistic-based Empirical Tight Binding calculations of electronic and optical properties of Nanowires, Quantum Dots and Quantum Wells
• Accurate ETB sp3s*d5 parameterization for several materials, including GaN/AlGaN/InGaN systems
• VCA and random alloy approach to treat in a fundamental way nanometric features in active regions, such as alloy fluctuations