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Nanoscale Solid-State Lighting Device Simulator

By Shaikh S. Ahmed1, Vinay Uday Chimalgi1, Katina Mattingly, Krishna Kumari Yalavarthi1

1. Southern Illinois University Carbondale

Simulates the electronic and optical properties of nanoscale solid-state lighting devices in III-N material systems

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Version 1.1 - published on 24 Jun 2015

doi:10.4231/D3DR2P94F cite this

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Abstract

Recently, optical emitters using InGaN nanostructures (quantum dots and nanowires) have attracted much at­tention for applications in lasers, solid-state lighting, solar cells, consumer displays, as well as diagnostic medicine and biological imaging. Compared to conventional bulk and quantum well (QW) structures, nanostructured devices offer several benefits as follow: 1) Strain in nanostructures is, to a large extent, re­laxed and, therefore, threading dislo­cations can be smaller leading to increased quantum efficiency; 2) The fact that the con­cen­tration of strain-induced defects is small in nanostruc­tures allows the use of higher indium content and more design freedom in bandgap engineering in the device, which poten­tially could lead to full-spectrum LEDs (as well as solar cells); and 3) Nanostructures used in the active region of optical devices provide im­proved elec­tron con­finement (due to strongly peaked energy dependence of den­sity-of-states) and thus higher temperature stability of threshold current and luminescence.

The great majorities of InN/GaN nanostructures crystal­lize in the ther­modynamically stable wurtzite symmetry and are grown along the polar [0001] direction. Since the het­eroepitaxy of InN on GaN involves a lattice mismatch of ~11%, these structures gener­ally exhibit atomically inhomo­geneous and long-range internal structural and electrostatic fields origi­nating mainly from: (i) the fundamental crystal atomicity and the interface discontinuity between two dissimilar materials, (ii) atomistic strain distribution, (iii) piezoelectricity, and (iv) spontaneous polarization (pyroelectricity). The magni­tude of the electrostatic built-in field has been estimated to be on the order of MV/cm. Such fields spatially separate the electrons and holes, which leads to a reduction in the optical transition rate (enhanced ra­diative lifetimes) and pronounced polarization anisotropy in optical emission/absorption. Therefore, electronic and optical properties of these nanostructures are expected to be strong functions of an intricate interplay between the atomistic struc­tural fields and the quantum mechanical size quantization effects.

The nanoSSL simulator allows one to study the electronic bandstructure and optical properties of wurtzite GaN/InN/GaN disk-in-wire structures. Using the simulator one can: (i) Explore the origin and nature of various built-in fields including crystal atomicity, strain fields, piezoelectric, and pyroelectric potentials; (ii) Quantify the role of these internal fields on the electronic bandstructure in terms of shift in energy levels and split (non-degeneracy) in the excited P states, and (iii) Demonstrate how the atomistically-calculated electronic structures lead to strongly suppressed optical transitions and pronounced growth-plane optical polarization anisotropy in these emerging reduced-dimensionality LEDs. 

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Credits

This work was supported by National Science Foundation Grant No. 1102192.

Support for the computational resources from the ORAU/ORNL High-Performance Computing Grant 2009 is also acknowledged.

Publications

  1. S. Sundaresan, V. Gaddipati, and S. Ahmed, “Effects of Spontaneous and Piezoelectric Polarization Fields on the Electronic and Optical Properties in GaN/AlN Quantum Dots: Multimillion-Atom sp3d5s* Tight-Binding Simulations,” Journal of Numerical Modeling, Wiley, published on 2 Jun 2014, DOI: 10.1002/jnm.2008.
  2. K. Yalavarthi, V. Chimalgi and S. Ahmed, “How Important is Nonlinear Piezoelectricity in Wurtzite GaN/InN/GaN Disk-in-Nanowire LED Structures?” Opt Quant Electron, vol. 46, pp. 925–933, 2014.
  3. K. Merill, K. Yalavarthi and S. Ahmed, “Giant Growth-Plane Optical Anisotropy in c-Plane Wurtzite GaN/InN/GaN Dot-in-Nanowires,” Superlattices and Microstructures, vol. 52, no. 5, pp. 949–961, November 2012.
  4. K. Yalavarthi, V. Gaddipati, and S. Ahmed, “Internal Fields in InN/GaN Quantum Dots: Geometry Dependence and Competing Effects on the Electronic Structure,” Physica E: Low-Dimensional Systems and Nanostructures, vol. 43, pp. 1235–1239, 2011.
  5. S. Ahmed, S. Islam, and S. Mohammed, “Electronic Structure of InN/GaN Quantum Dots: Multimillion Atom Tight-Binding Simulations,” IEEE Trans. Electron Devices, vol. 57, no. 1, pp. 164–173, 2010. 

Cite this work

Researchers should cite this work as follows:

  • Shaikh S. Ahmed; Vinay Uday Chimalgi; Katina Mattingly; Krishna Kumari Yalavarthi (2015), "Nanoscale Solid-State Lighting Device Simulator," http://nanohub.org/resources/nanossl. (DOI: 10.4231/D3DR2P94F).

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