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

Abstract

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.