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

D.-H. Lee1, D. Kang2, T.-Y. Seong1,3,6, M. Kneissl4,5 and H. Amano6

Published in:

J. Phys. D: Appl. Phys., vol. 53, no. 04, pp. 045106 (2020).

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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 µm) were fabricated with flip-chip structures. It was shown that at 4 A cm-2, the forward voltages of 300 µm-size and 10 µm-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 µm-size LEDs displayed maximum external quantum efficiency (EQE) at 2 A cm-2), whereas the 10 µm-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 µm-size LEDs, the 10 µm-size LEDs exhibited a large deviation in the light output, EQE, and EL wavelength. The 10 µm-size LEDs revealed larger S than the 300 µm-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.

1 Department of Nanophotonics, Korea University, Seoul 02841, Republic of Korea
2 LED Division, LG Innotek Co., Ltd., Paju, Gyeonggi 10842, Republic of Korea
3 Department of Materials Science and Engineering, Korea University, Seoul 02841, Republic of Korea
4 Institute of Solid State Physics, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany
5 Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin, Germany
6 Centre for Integrated Research of Future Electronics, and Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya 464-8603, Japan

Keywords:

micro-light emitting diode, V pit size, cathodoluminescence.