Experimental and theoretical study of electrical, thermal, and optical characteristics of InGaN/GaN high-power flip-chip LEDs

Comprehensive analysis of current spreading, temperature distribution, and near-field electroluminescence (EL) of high-power flip-chip InGaN/GaN light-emitting diodes (LEDs) has been performed by combination of experimental and theoretical methods. High-resolution mapping of EL and thermal radiation was obtained by optical and infra-red (IR) microscopes. Thermal resistance of the chip was measured by forward-voltage relaxation technique. 3D coupled electrical, thermal, and optical simulations were carried out using hybrid 1D/3D model. The theoretical predictions agree well with available observations. The lateral distributions of the near-field EL intensity and temperature are found to be qualitatively similar to that of the current density but to have substantially lower degree of non-uniformity. Therefore, it becomes incorrect to judge the current crowding in the LED chip by the measured contrast of the EL image. The role of contact resistances in stabilization of the current spreading pattern is revealed by modeling.