Opto-electronic Simulation of GaN Nanowire Lasers
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Opto-electronic Simulation of GaN Nanowire Lasers Liang Chen 1 and Elias Towe Department of Electrical and Computer Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, U.S.A. 1 RSoft Design Group, Inc., 400 Executive Blvd., Ossining, NY 10520, U.S.A. ABSTRACT A coupled opto-electronic simulation for studying GaN nanowire lasers is presented. The model solves carrier transport equations and photon rate equations self-consistently. The basic physical model takes into account both bulk and surface dark recombinations, stimulated emission, the anisotropic optical gain typical of the Wurtzite GaN structure, the modified spontaneous emission, and its coupling into the lasing modes by microcavity effects. The model further incorporates band gap shrinkage effects due to band renormalization and the effects of multiple lateral and longitudinal lasing and non-lasing optical modes. INTRODUCTION Semiconductor nanowires are one-dimensional structures that can be synthesized via chemical processes [1]. Through proper control of the growth process parameters, doping, and other materials parameters, one can create unique electronic and optical properties [2-12]. These wires have several potential applications; the particular application of interest in photonics is in microcavity lasers [6-9] based on high-quality single crystalline nanowires. Various nanowire lasers synthesized from GaN, ZnO, and CdS have been demonstrated in recent years. The lightemitting capability of the nanowires, combined with their other unique features which arise due to their one-dimensionality, make them particularly interesting to consider as candidates for components of future nanoscale photonic systems. In general, the semiconductor nanowire lasers are synthesized along specific crystallographic directions by chemical processes with catalysts attached to the front end of a growing seed [1]. A typical lateral dimension of a nanowire is between 20 ~ 400 nm, with a length that ranges from 2 ~ 40 µm. In this size range, and because of the high dielectric constant contrast between the nanowire material and the surrounding ambient, a strong lateral optical confining effect is created that results in the waveguiding of the light along the axial direction. Since nanowires are single-crystalline, the end facets can form natural mirrors at either end of the wire [6-9]. These form an axial Fabry–Perot type cavity necessary for laser action. To appreciate the initimate coupling between the electronic and optical properties in the nanowire laser structures, one needs detailed knowledge of how light interacts with the charge carriers in the structure. In this paper, we provide a detailed discussion of the modeling, calculations, and analysis of the optical and electronic properties of the GaN nanowire lasers. COUPLED OPTO-ELECTRONIC SIMULATION In the coupled opto-electronic simulation, a single GaN nanowire is assumed to be a thin uniform cylinder and have both end facets open to the air. The pumping is by optical excitation
0892-FF11-08
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