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Deepen

atom-to-Device Explicit simulation
Environment for Photonics and
Electronics Nanostructures
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Scientific & Technical Overview

DEEPEN addresses problems common to future nanoscale electronic and photonic devices, providing an atomic-scale description of selected critical regions e.g. in the channel of a nanoscale transistor or active region of an LED while using continuum-level electronic models to describe the full device structure. DEEPEN also addresses the considerable uncertainty in many critical parameters required for device optimization.

DEEPEN will develop an open multi-scale modelling environment to simulate electronic transport processes in nanoelectronic and nanophotonic devices. The simulations will treat critical device regions using ab-initio calculation techniques, or, for larger critical regions, using empirical (tight-binding) methods. The interface between models is designed to be open and re-usable with a wide range of existing codes. An open source Common Data Format (CDF) is being defined, and relevant metadata keywords will be defined in order to allow the exchange of data of different kinds (mesh associated or global quantities, physical and geometrical parameters). The environment will be demonstrated by integrating a range of open source and proprietary codes (electronic and continuum), which have the well-established capability to calculate phenomena at different levels of description. Although demonstrated with specific codes, it is envisaged that the interface should also be usable across a range of other codes with suitable adaptation of the code linkages to the interface.  The figure below shows an example workflow of some of the different types of model being linked in DEEPEN.

 

Summary of Modelling

DEEPEN will implement linking and coupling schemes for a range of different models from ab-initio through to empirical tight binding and charge carrier diffusion codes.

Linking models

Several models will be linked (i.e. loosely coupled), with the output from the lower level being used to determine the input for higher level models. First principles electronic structure calculations will be used to determine details of carrier localisation. These empirical local electronic structure calculations will then be incorporated into a generic tight binding (TB) model applied to vertical transport and will also form the basis for a hopping model to describe lateral transport in InGaN quantum well structures. Linked simulations of TB code OMEN and continuum (device) code SENTAURUS will use parameters extracted from more detailed studies performed on smaller structures, including ab-initio calculations.

Coupling models

In order to accurately describe selected nanoscale regions, model coupling will be implemented between a first principles density functional theory (DFT) code such as VASP and code OMEN the DFT-based transport code TiMeS. Both "transport codes" will be set up to accept Hamiltonian input in a tight-binding DFT format e.g. directly from OpenMX or from VASP, with the VASP plane-wave output converted to a localised basis using e.g. Wannier90. The output from the transport codes will then be fed back to the DFT codes to allow self-consistent calculation of the electronic structure and transport properties. Coupled simulations of OMEN and Sentaurus Device will be used when feedback effects from the macroscopic level to the nanoscale (e.g. by electrostatic interactions) are important in electronic devices, and fully self-consistent simulation of the system may be required. Coupling of models will also be required to investigate carrier tunnelling between neighbouring quantum wells in a multi-quantum well LED structure. The electronic tunnelling models will be implemented by developing TiMeS to treat tunnelling through the barrier between neighbouring quantum wells. To investigate the role of inter-well tunnelling in determining the steady-state carrier distribution in a MQW structure, this tunnelling model will be tightly coupled to TIBERLab’s software, TIBERCAD as an example of an existing drift diffusion code

Interfaces and Platform

TiberCAD as well as S-Device are closed-source commercial products. The general output format which we are developing should be adaptable for use with open source TCAD software, which could be used as a substitute. The interface developed in DEEPEN will be open source, allowing others to use existing commercial software or to adapt open source TCAD software for use with the DEEPEN platform. Together with 5 other NMP projects on multi-scale modelling (ICMEg, MMP, MODENA, NANOSIM and SIMPHONY) communication standards (metadata keywords and an overall data structure for file based information exchange) will be elaborated. These will be used in the DEEPEN platform.The cluster of projects are organising workshops to reach European endorsement. Once established, the platform will be widely applicable across a wide range of applications. The project’s OS environment will be released under the GNU Lesser General Public License (GNU LGPL), ensuring that the core of the multiscale environment together with all its Application Programming Interfaces (APIs) can be distributed and even modified freely. It will also be available through TIBERLab’s existing support environment www.tibercad.org .