Characteristics of flip-chip InGaN-based light-emitting diodes on patterned sapphire substrates

We report on the characteristics of high-power near-ultraviolet (425 nm) flip-chip InGaN light-emitting diodes (LEDs) fabricated onto a patterned sapphire substrate (PSS). When the PSS flip-chip LED (chip size: 1 mm(2)) operated at a 20 mA forward current at room temperature, the forward voltage and the light output power were 3.15 V and 6.8 mW, respectively. It was found that the PSS flip-chip LED has similar current-voltage characteristics to those of a conventional flip-chip LED. The luminance intensity of the PSS flip-chip LED was approximately 43% lager than that of the conventional flip-chip LED (at 100 mA). Moreover, the light output power was greatly increased by 59% for the PSS sample at a forward injection current of 350 mA compared with that of the conventional flip-chip LED. This result was attributed to the increase in the probability of photons escaping from the LED samples, resulting in the enhancement of light extraction efficiency. The effect of the PSS on the flip-chip LED structure has been simulated and shows a good correlation with the measured results.