A Comparative Study of Thermal Metrology Techniques for Ultraviolet Light Emitting Diodes

Abstract

Methods used to measure the temperature of AlxGa1−xN based ultraviolet light emitting diodes (UV LEDs) are based on optical or electrical phenomena that are sensitive to either local, surface, or average temperatures within the LED. A comparative study of the temperature rise of AlxGa1−xN UV LEDs measured by microRaman spectroscopy, infrared (IR) thermography, and the forward voltage method is presented. Experimental temperature measurements are provided for UV LEDs with micropixel and interdigitated contact geometries, as well as for a number of different packaging configurations. It was found that IR spectroscopy was sensitive to optical properties of the device layers, while forward voltage method provided higher temperatures, in general. Raman spectroscopy was used to measure specific layers within the LED, showing that growth substrate temperatures in the flipchip LEDs agreed more closely to IR measurements while layers closer to the multiple quantum wells (MQWs) agreed more closely with Forward Voltage measurements.