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. 

QuaDS 3-D and NEMO 3-D

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 and NSF CRI 0855221 are also acknowledged.

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Researchers should cite this work as follows:

• Shaikh S. Ahmed, Vinay Uday Chimalgi, Katina Mattingly, krishna kumari Yalavarthi, Rezaul Karim Nishat (2019), "Nanoscale Solid-State Lighting Device Simulator," https://nanohub.org/resources/nanossl. (DOI: 10.21981/3BN4-CR53).

  BibTex | EndNote

1. nanoelectronics
2. Nitride LEDs