Junction Temperature Measurements in Deep-UV Light-Emitting Diodes
- PDF / 512,795 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 108 Downloads / 207 Views
E1.7.1
Junction Temperature Measurements in Deep-UV Light-Emitting Diodes Y. Xia, J.-Q. Xia, Th. Gessmannb, J. M. Shahb, J. K. Kimb, E. F. Schuberta,b*, A. J. Fischerc, M. H. Crawfordc, K. H. A. Bogartc, and A. A. Allermanc The Future Chips Constellation a Department of Physics, Applied Physics, and Astronomy b Department of Electrical, Computer, and Systems Engineering Rensselaer Polytechnic Institute, Troy, NY 12180 c Compound Semiconductor Research Laboratory, Sandia National Laboratories, Albuquerque, NM 87185
ABSTRACT The junction temperature of AlGaN/GaN ultraviolet (UV) Light-Emitting Diodes (LEDs) emitting at 295 nm is measured by using the temperature coefficients of the diode forward voltage and emission peak energy. The high-energy slope of the spectrum is explored to measure the carrier temperature. A linear relation between junction temperature and current is found. Analysis of the experimental methods reveals that the diode-forward voltage is the most accurate method (± 3 °C). A theoretical model for the dependence of the diode junction voltage (Vj) on junction temperature (T) is developed that takes into account the temperature dependence of the energy gap. A thermal resistance of 87.6 K/W is obtained with the AlGaN/GaN LED sample mounted with thermal paste on a heat sink. INTRODUCTION III–V nitride semiconductors have a direct bandgap and thus are very suitable for solid-state ultraviolet light sources. Such UV sources have a wide variety of applications, including UVinduced fluorescence, sanitation, communications, photo-catalytic processes, high resolution optics, lighting, and displays. Double heterostructure GaInN/AlGaN UV LEDs emitting at 371 nm with external quantum efficiency of 7.5 % and output powers of 5 mW have been demonstrated1. In the deep UV, devices emitting 1.3 mW at 290 nm were recently demonstrated by Sandia National Laboratories2. The junction temperature is a critical parameter and affects internal efficiency, maximum output power and reliability. Several groups have reported measurements of the junction temperature of laser diodes (LDs) using micro Raman spectroscopy3, threshold voltage4, thermal resistance5, photothermal reflectance microscopy (PRM)6, electroluminescence7, photoluminescence8. A non-contact method based on the emission peak ratio has been demonstrated for a white dichromatic LED source9. THEORY From the well-known Shockley equation, for a junction voltage Vj >> kT/e, we obtain dV j dT
=
d dT
⎡ nideal kT ⎛ J j ⎞⎤ ln ⎜⎜ ⎟⎟⎥ , ⎢ e ⎝ J s ⎠⎦⎥ ⎣⎢
(1)
where Js is the saturation current density, nideal is the diode-ideality factor, and the other symbols have their usual meaning10. The saturation current density depends on the diffusion constants of *
Electronic email: [email protected]
E1.7.2
electrons and holes, the lifetimes of electrons and holes, the effective density of states at the conduction band and valence band edge, and the bandgap energy, all of which depend on the junction temperature. Substituting the temperature-dependences of these quantities
Data Loading...
