Influence of Size reduction and Current Density on the Optoelectrical Properties of Green III-Nitride Micro-LEDs

We have investigated the effect of chip size on the forward voltage, light output, emission image and spectral shift of InGaN based green LEDs (518 nm) as a function of current density. The size of the chips was varied from 10 to 100 mu m. The smaller chips exhibited higher light output power although the lower output powers were obtained at the higher current densities. Furthermore, the smallest devices showed the better current spreading at higher current densities. It was shown that green micro-LEDs (mu LEDs) experienced spectral shift when drive current and chip size increased, but the shift was more significantly dependent on dc drive current compared with chip size. The relation between the electroluminescence characteristics and current density of different-size devices revealed that the devices more dominantly went through blue shift than red shift. However, at the same current density, the peak of the devices was not shifted when the device size changed. Dependence of the chip size and current density on the spectral shift of green mu LEDs will be described and discussed in terms of effects of band-filling and stress relaxation.