Combined effects of V pits and chip size on the electrical and optical properties of green InGaN-based light-emitting diodes

The fabrication of ultra-high-resolution micro-displays with low power consumption is essential for applications in virtual reality and augmented reality systems. In this regard, GaN-based light-emitting diodes (LEDs) have been regarded as a promising candidate for self-emissive micro-displays. However, micro-LEDs suffer from sidewall defects and low quantum efficiency at a low current. Thus, we investigated the electrical and optical properties of InGaN-based green (520 nm) LEDs as functions of V pits and chip size. With decreasing chip size, the forward voltage of all samples increased at the same injection current. The samples with V pits exhibited markedly higher current density than those without V pits. With decreasing chip size, the current densities of all the samples increased, whereas the output power at the same current density decreased. As the chip size decreased, the peak external quantum efficiency of all the samples decreased, which was attained at high current densities. Furthermore, the samples with V pits displayed more efficient current spreading behavior, smaller ideality factors, and a smaller S parameter than the ones without V pits. The emission wavelength of the small samples (<300 μm) was blue-shifted with increasing current density. Based on the cathodoluminescence results, the effects of chip size, current density, and V pits on the electroluminescence spectral shift of green LEDs are described and discussed.