Improving Accuracy of Temperature Mapping of High-Power AlInGaN LED Chips

Comprehensive analysis of current spreading, temperature distribution, and near-field electroluminescence of high-power "face-up" AlInGaN LEDs been performed by a combination of different experimental methods. A thermal resistance characterization consists in investigations of transient electrical processes in the diode sources under heating by direct current and analysis using a thermal equivalent circuit (the Cauer model). By the involved method, thermal resistances of internal elements of the LEDs are determined. At the same time, high-resolution mapping of EL and thermal radiation was obtained by an optical microscope and infrared images technique To obtain the temperature distribution inside the chip, the infrared (IR) thermal radiation in the spectral range of 2.5-3 mu m was mapped by a specially designed IR-microscope. To increase the accuracy the temperature mapping, a new measurement technique using a special coating which combines strong absorption in the region of sensitivity of IR-microscope and transparency in the visible region of the LED emission was applied. It has been established a correlation between the thermal resistance and change in the current distribution at high excitation levels (current crowding).