Jianchang Yan*1,2, Yanan Guo1,2, Tongbo Wei1,2, Zhiqiang Liu1,2, Junxi Wang1,2, Jinmin Li1,2

1 Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China,

2 Center of Materials Science and Optoelectronics Engineering，University of Chinese Academy of Sciences, Beijing 100049, China.

*Email: yanjc@semi.ac.cn

 

AlGaN-based deep-ultraviolet lighting-emitting diodes (DUV LEDs) have been regarded as the next-generation DUV light sources operating at wavelength below 300 nm thanks to their advantages such as compact size, robustness, environmental friendliness, low operating voltage and tunable wavelength. However, the general quantum efficiency of DUV LEDs is less than 10%, which postpones their widespread application. The limited efficiency is mainly attributed to the limited material crystalline quality and the poor light extraction efficiency (LEE). Quasi-Van der Walls epitaxy of AlN and AlGaN on two-dimensional (2D) layered materials, such as graphene and hexagonal boron nitride (h-BN), has attracted increasing attention because it promises stress-free and low dislocation growth. Due to the weak Van der Waals interaction within 2D layers, the 2D materials can also act as a mechanical release layer for LEDs with negligible damage, thus enables improved LEE and thermal management.

h-BN is a III-nitride compound possessing a similar honeycomb lattice structure to graphene, but with a wider bandgap, better stability and fabrication system compatibility. Nevertheless, the lack of dangling bonds or nucleation-site-like defects on the h-BN surface makes the growth of high quality Al(Ga)N films not an easy job. Herein, we present the research into growth of crystalline AlN and high-performance DUV LEDs on h-BN/sapphire substrates by metal-organic chemical vapor deposition (MOCVD). Oxygen plasma was implanted to the monolayer h-BN surface, transferring some hybridization orbitals of B atoms from sp2 into sp3, which would lower the nucleation energy of AlN. The edge dislocation density of AlN on O2-treated h-BN was reduced by 35% compared to that of AlN on untreated h-BN. A reasonable growth model was proposed to explain the growth mechanism and dislocation behavior of AlN on O2-treated and untreated h-BN[1]. The compressive stress in the epitaxial AlN on O2-treated h-BN was significantly released. The AlGaN-based DUV LED on such AlN/h-BN/sapphire exhibited desirable deice performance with a maximum light output power of 1.458 mW at 115 mA[2].

To further realize the exfoliation of epilayers, we employed alternative multilayer h-BN (~3 nm) deposited on sapphire in wafer scale by MOCVD. The AlN film grown the multilayer h-BN showed a flat and smooth surface morphology. The full width at half-maximum values were 1086 and 3240 arcsec for (0002) and (10-12) X-ray diffraction rocking curves, respectively, illustrating the crystalline status of the AlN film[3]. On the high-quality AlN film, DUV LEDs with strong electroluminescence at a peak wavelength of 281 nm and low leakage current were obtained. With the aid of carbon flexible tape, the AlN film and LEDs on multilayer h-BN were successfully exfoliated. It is promising that the multilayer h-BN will pave the way to obtain transferable high-efficiency devices with wafer scale.

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[1] Wu Q., Yan J., Zhang L. et al. CrystEngComm, 2017, 19(39): 5849-5856.

[2] Li Q., Wu Q., Gao J. et al. Advanced Materials Interfaces, 2018, 10.1002/admi.2018006621800662.

[3] Wu Q., Guo Y., Sundaram S. et al. Applied Physics Express, 2019, 12(1): 015505.