Towards a Novel Broadband Spectrally Dynamic Solid State Light Source
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Towards a Novel Broadband Spectrally Dynamic Solid State Light Source David B. Nicol1, Shalini Gupta1, Nola Li1, Ali Asghar2, Elton Graugnard3, Chris Summers3, Ian T. Ferguson1,3 1 School of Electrical and Computer Engineering Georgia Institute of Technology Atlanta, GA 30332, U.S.A. 2 EMCORE Corporation 394 Elizabeth Avenue Somerset, NJ 08873, U.S.A. 3 School of Material Science Engineering Georgia Institute of Technology Atlanta, GA 30332, U.S.A. ABSTRACT The developments of two major components of a three terminal dual wavelength LED for excitation of multiple phosphors are described. Such a configuration will be novel Broadband Spectrally Dynamic Light Emitting Diode (BSDLED). First, work towards a functional tunnel junction in the GaN system is discussed. The developments of p+ and n+ GaN layers are specifically discussed in relation to their use in a buried current spreading contact layer. Second, the analysis of several phosphors and their application in a spectrally dynamic source is explored. The response to multiple wavelengths of the phosphors is analyzed to create a light source that can be tuned in “real time” to a wide range of correlated color temperatures. INTRODUCTION The lighting industry is on the cusp of a major revolution with the development of new illumination sources based on light emitting diodes (LEDs) which has become known as solid state lighting (SSL)[1]. Traditionally, LEDs have been used as indicator lights, replacing small incandescent lamps and have only recently become widespread in niche applications such as signage, backlighting, mobile devices, traffic signals, and large area displays. In these applications one or more of the following key attributes make solid state sources attractive alternatives to conventional illumination technologies: saturated color, small size, energy efficiency, robustness, and controllability. However, no significant penetration has been achieved in general illumination where different criteria such as broadband, high color rendering capability, and appropriate correlated color temperature make the adoption of SSL more difficult. In fact, in many cases designers and architects are seeking added functionality such as dynamic spectral control. Thus, there is a need to develop novel devices that lend themselves to a SSL general illumination solution. A dual wavelength LED coated with a combination of phosphors, Figure 1, that allows for a broadband spectrally dynamic source is described here that may fit many of the criteria for a successful solid state light source. This work envisions a three terminal LED with two active regions capable of separate control, pumping multiple phosphors to create a broadband emission with a dynamic spectral power distribution. Separate
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control via three terminals may be achieved with the use of a buried tunnel junction in the device.
Figure 1. One possible device schematic of a BSDLED with the topmost layer being the combination of phosphors.
Dual wavelength LEDs and conventional LEDs inc
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