In situ temperature measurements via ruby R lines of sapphire substrate based InGaN light emitting diodes during operation

The temperature of encapsulated green and ultraviolet light emitting diodes (LEDs) in operation has been measured optically via the ruby R lines emitt ed by the residual Cr3+ contaminations in the sapphire substrate. These two photoluminescent R lines, which are excited by the electroluminescence of the LED itself, show a well-characterized line shift as a function of tempe rature and pressure. The temperature is found to rise linearly with the app lied forward current of the LED at a rate of approximate to1 K/mA. This opt ical temperature measurement based on monitoring the two ruby R lines could qualify as a sensitive method for an in situ temperature sensor for other sapphire substrate based semiconductor devices such as laser diodes and fie ld effect transistors. (C) 2001 American Institute of Physics.