Development of junction temperature estimation system for light-emitting LED using pulsed-laser Raman scattering

Abstract

A new method by using a pulsed-laser Raman scattering technique was employed to estimate junction temperature of a fluorescence-resin-less blue-LED package. Temperature dependent Raman shift of E 2 H mode of GaN layer in the blue-LED were obtained and were in good agreement with the experimental data published by the other researchers. This technique was applied to estimation of a junction temperature of the light-emitting blue-LED. The junction temperature was successfully estimated even under the strong stray light and LED light emission. It is considered that the proposed technique would be a remote and standard system for measuring the junction temperature of light-emitting white-LEDs.

The Development of a System for Measuring the Junction Temperatures of Multiple LEDs on a Package Simultaneously by Using Pulsed-laser Raman Scattering

“…T is the absolute temperature, h is the Planck constant, c is the speed of light in a vacuum, ω 0 is the Ra-man phonon frequency at 0 K, k B is the Boltzmann constant while A and B are the fitting parameters 4) . For the E 2 H mode, they give ω 0 568.2 0.2 cm 1 , A 17.9 2.4 cm 1 , and B 0.99 0.08, where the experimental data obtained by them in the temperature range of 90-770 K and our previous data (300-450 K) 14) are well reproduced by this formula.…”

“…Under these situations, we have been developing a pulsed-laser Raman scattering method as a remote and standard method for measuring the junction temperature of a light-emitting phosphor-resin coated blue-LED [13][14][15] where the Raman shift of the E 2 H mode of the GaN layer (GaN-E 2 H ) is observed. Using a nanosecond pulsed-laser as an incident light source, sufficient laser power density for the detection of weak Raman signals can be achieved even on a relatively large irradiation area of an LED package placed far from the laser injection and scattering light detection optics, instead of a CW laser being focused on to a very small area.…”

“…In the previous paper, we described the observation of Raman spectra from one of several chips on a phosphor-less blue-LED by the pulsed-laser Raman scattering method. It was shown that the Raman shift of the E 2 H mode of the GaN layer of the blue LED chip was dependent with the temperature and that the junction temperature of the chip in operation was done successfully despite the existence of intense stray light, Rayleigh scattering and LED emission 14) .…”

“…The pulsed-laser Raman scattering system and the experimental procedure are very similar to the methods described in the previously-presented papers 13,14) . A dye laser beam of 632.816 nm, which was pumped by the SHG of a Nd:YAG laser, was passed through a laser line filter to remove amplified spontaneous emissions included in it.…”

“…The junction temperatures can be estimated not only by the Raman shift but also by the intensity ratio of stokes and anti-stokes of peak 1) . In this study, due to the functional limitation of the optics, the junction temperature estimation was made only from the shift of the Raman peak 14) . The formula of the temperature dependence of the Raman shift in GaN, which is given by Liu et al, is as follows:…”