Effect of unevenly-distributed V pits on the optical and electrical characteristics of green micro-light emitting diode

In this study, we investigated the effect of different-size V pits on the opto-electrical performance of different-size InGaN-based green (520 nm) light-emitting diodes (LEDs). The size of V pits varied from 57 to 250 nm. Two different-size LEDs (10 and 300 m) were fabricated with flip-chip structures. It was shown that at 4 A cm^-2, the forward voltages of 300 m-size and 10 m-size LEDs were in the range of 2.32-2.82 V and 2.23-2.53 V, respectively. Compared with the LEDs with small V pits, the LEDs with large V pits produced higher output power at the high current region (>50 A cm^-2), but lower output power at the low current region (<20 A cm^-2). The 300 m-size LEDs displayed maximum external quantum efficiency (EQE) at 2 A cm^-2, whereas the 10 m-size LEDs exhibited peak EQE at current densities 13 A cm^-2. For all samples, the electroluminescence (EL) wavelengths were blue shifted with increasing current density. Unlike the 300 m-size LEDs, the 10 m-size LEDs exhibited a large deviation in the light output, EQE, and EL wavelength. The 10 m-size LEDs revealed larger S than the 300 m-size LEDs. The backscattered electron (BSE) and monochromatic cathodoluminescence (CL) results showed that for all samples, V pits were unevenly distributed across the whole wafer. Based on the CL and BSE results, the effect of different V pit sizes on the performance of green micro-LEDs at the low current region is described and discussed.