Optoelectronic and thermal characteristics of GaN-based monolithic light emitting diode arrays

We investigated the optoelectronic and thermal characteristics of InGaN/GaN monolithic light emitting diode (LED) arrays operating at lambda similar to 470 nm. The optical output power (P-out) and forward voltage (V-F) were almost linearly increased with the number of LEDs for series arrays. In the case of parallel LED arrays, the maximum operating current was increased by increasing the number of devices, but the V-F was kept almost constant. Around 235 mA, the maximum P-out of 55.6 mW was obtained for the 1 x 3 series LED array fabricated with a separation distance of 1000 mu m, while the P-out was 20.4 mW for the 1 x 3 parallel LED array. From the measured light-current-voltage data, the maximum internal temperature (T-max), i.e. a maximum value of internal temperature rise within the devices under operation, was theoretically determined using a three-dimensional steady-state thermal heat dissipation model based on the finite element method. Also, the temperature profiles were obtained for various separation distances and array sizes. At injection current of 220 mA, the T-max was theoretically calculated as 325.6 K and 306.6 K for 1 x 3 series and parallel LED arrays with a 1000 mu m separation distance, respectively. The T-max was increased and decreased on decreasing the separation distance and substrate thickness, respectively, and its dependence on T-max became more significant at higher injection current.