Hexagonal Pyramids Shaped GaN Light Emitting Diodes Array by N-polar Wet Etching
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Hexagonal Pyramids Shaped GaN Light Emitting Diodes Array by N-polar Wet Etching Jun Ma*, Liancheng Wang, Zhiqiang Liu, Guodong Yuan, Xiaoli Ji, Ping Ma , Junxi Wang, Xiaoyan Yi, Guohong Wang and Jinmin Li Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, P R China ABSTRACT In this work, we investigated the influence of N-polar wet etching on the properties of nitride-based hexagonal pyramids array (HPA) vertical-injection light emitting diodes (V-LEDs). The cathodeluminescence images showed the randomly distribution of hexagonal pyramids with isolated active regions. The transmission electron microscopy images demonstrated the reduced density of threading dislocations. The IQE was estimated by temperature dependence of photoluminescence, which showed 30% increase for HPA V-LEDs compared with broad area (BA) V-LEDs. The improved extraction efficiency was verified by finite difference time domain simulation, which was 20% higher than that of roughened BA V-LEDs. The electrical properties of HPA V-LEDs were measured by conductive atomic force microscopy (CAFM) measurements. HPA V-LEDs exhibited much lower leakage current due to the improved crystal quality. INTRODUCTION Nitride-based vertical-injection light emitting diodes (V-LEDs), of which the insulated sapphire substrates were substituted by the Cu substrates, have been believed to be a promising candidate for high power applications.[1,2,3] Due to the thermal, electrical conductivity of Cu submount and the vertical current injection, V-LEDs have the advantages of better current injection, excellent heat dissipation, superior electrostatic discharge protection, and simple packaging process.[4,5] However, the development of V-LEDs for high power applications still suffers from severe obstacle, such as large reversed leakage current, serious efficiency droop and limited light extraction. Recently, remarkable advances in the low-dimensional nanostructure LEDs seem to provide an inspiring solution. In particular, the nanowire/nanorod GaN LEDs have brilliant quantum efficiency and improved efficiency droop. [6,7] On the other hand, N-polar (000 ) surface wet etching process has been commonly adopted to acquire the textured surface in order to improve the extraction efficiency in the fabrication of conventional GaN broad area (BA) V-LEDs.[8] The hexagonal pyramid-shaped morphology produced on the N-polar face during the wet etching process has been reported by several groups.[9,10,11] It is believed that threading dislocations (TDs) serve as nucleation points for the etch process, and other defects play an important role in the wet etching of N-polar (000 ) surface.[12,13] In this paper, we presented the fabrication of hexagonal pyramids array (HPA) V-LEDs. The hexagonal pyramids with isolated active regions were produced by the N-polar (000 ) face wet etching. The eliminating of TDs in hexagonal pyramids was realized by the wet etching process. The electrical and optical properties of HPA V-LEDs were investigated. Compared with conventional BA V
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