Colloidal quantum dot active layer electroluminescence in a solid GaN matrix
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0891-EE03-06.1
Colloidal quantum dot active layer electroluminescence in a solid GaN matrix Jennifer Pagan1, Edward Stokes2, Kinnari Patel, Casey Burkhart, Mike Ahrens1 Department of Electrical and Computer Engineering, The University of North Carolina at Charlotte, Charlotte, NC 28223-001, U.S.A. 1 Dot Metrics Technologies, 9201 University City Boulevard, Charlotte, NC 28223-0001, USA 2 Center for Optoelectronics and Optical Communications, Charlotte Research Institute, Charlotte, NC 28223-0001, USA
ABSTRACT In this paper the preliminary results of incorporating a novel active layer into a GaN light emitting diode (LED) are discussed. Integration of colloidal CdSe quantum dots into a GaN LED active layer is demonstrated. The conductivity of the overgrowth was examined by circular transmission line method (CTLM). Effects on surface roughness due to the active layer incorporation are examined using atomic force microscopy (AFM). LED test devices were fabricated and electroluminescence was demonstrated, the devices exhibit higher turn-on voltages than would be expected for a CdSe active layer.
INTRODUCTION Nanotechnology is proliferating at a rapid rate in many areas including semiconductor lasers, biotechnology, and optoelectronics, as researchers explore applications which capitalize on the unique advantages afforded them by operating on the nanoscale. In the case of semiconductor lasers it was found that by creating active layers on order of the de Broglie wavelength in all spatial directions, the movement of the free electrons would be restricted. This electron confinement inhibits the spreading of carriers thereby reducing the thermal sensitivity of a device [1, 2]. Quantum dots (QDs) are one representation of a semiconductor system where there is three dimensional carrier confinement, and as a result the emission spectrum of a QD can be tuned across a wide range of wavelengths due to the quantum size effect [3]. The ability of colloidal QDs to emit at wavelengths that are currently difficult to create efficiently using traditional LED material systems makes the technology ideal for use in LEDs. Semiconductor materials from the III-V group are used in high-efficiency LEDs at both ends of the visible spectrum, III-Arsenide-Phosphide (III-AsP) materials provide emission from yellow to infrared, and III-Nitride (III-N) materials emit from blue-green into the ultraviolet. However, there is no material in either the III-AsP or III-N material systems that provides efficient deep green (555585nm) emission. Highly efficient deep green colloidal CdSe quantum dot emitters are available however, and it has been recently suggested to use these colloidal quantum dots as the active layer in a GaN heterostructure (see Figure 1) to create a LED [4]. Presented are efforts to integrate colloidal quantum dots into GaN heterostructures to act as electroluminescent centers forming the active layer of a LED.
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p-GaN
n-GaN
sapphire Figure 1. Proposed LED heterostructure incorporating colloidal CdSe quantum dots as
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