Cooper, J D

Grier, A

Harrison, Paul

Valavanis, A

Sheffield Hallam University Research Archive

Quantum wells, wires and dots (QWWAD): development of anopen-source simulation suite for semiconductor nanostructuresA. Valavanis,a,1 J. D. Cooper,1 A. Grier,1 and P. Harrison,21School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK2Materials and Engineering Research Institute, Sheffield Hallam University, S1 1WB, UKa)Email: a.valavanis@leeds.ac.ukA number of robust software tools are available for simulating semiconductor nanostructures,including purpose-made products  such as Nextnano [1] and generic  finite-element  solverssuch as  COMSOL Multiphysics [2].  Although the  existing  tools  are  highly  regarded,  themajority of available software is supplied under a proprietary license, meaning that its sourcecode  cannot  be  studied,  modified  or  redistributed  freely  by  its  users.  As  such,  there  iscurrently  a  lack  of  free  software  for  students  wishing  to  learn  the  mathematical  andcomputational techniques that underpin modern nanoscale semiconductor physics.We present a non-commercial, free-and-open-source project, Quantum Wells, Wires and Dots(QWWAD) [3],  which  is  released  under  the  GNU  General  Public  License  3.0 [4].  Thissoftware  accompanies  the  forthcoming  4th edition  of  the  eponymous  textbook [5],  andincludes analytical and numerical solvers for the Schrödinger and Poisson equations, subbandpopulations, tunnelling and scattering phenomena, diffuse structures, impurity and excitonstates, and effective-mass and pseudopotential models of quantum wires and dots.In this paper, we explain our design methodology and software engineering approach, andgive an overview of the calculations that are included in the simulation suite. In particular, wefocus on the adoption of automated testing, which ensures the reliability of the underlyingcalculations  in  the  software,  and  on  the  provision  of  a  large  number  of  computationalexamples, enabling the use of the software as an educational tool. Fig. 1 shows exemplarplots of the data generated by these example scripts. Finally, we discuss the development ofan application programming interface (API), enabling the functionality in QWWAD to beadopted easily into other free software tools.(a) (b) (c)Fig. 1: Sample plots of the output data from the QWWAD educational example scripts. (a) The firstthree eigenstates in a finite GaAs quantum well. (b) Density of states in 200-Å GaAs infinite wellassuming parabolic dispersion (solid lines) and nonparabolic dispersion (dashed lines). (c) Effect ofcarrier  temperature  on  quasi-Fermi  levels  in  an  infinite  quantum  well,  with  a  range  ofnonparabolicity factors.References [1] Nextnano., http://www.nextnano.de/[2] COMSOL Multiphysics, http://www.uk.comsol.com/[3] Quantum wells, wires and dots, https://launchpad.net/qwwad[4] GNU General Public License 3.0, Free Software Foundation (2007) https://www.gnu.org/copyleft/gpl.html[5] P. Harrison and A. Valavanis, Quantum Wells, Wires and Dots, 4th Ed. Wiley, Chichester, (in preparation).

Quantum Wells,wires and dots (QWWAD): development of an open-source simulation suite for semi-conductor nanostructures

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