Abstract
High-quality and crack-free aluminum nitride (AlN) film on sapphire substrate is the foundation for high-efficiency aluminum gallium nitride (AlGaN)-based deep ultraviolet light-emitting diodes (DUV LEDs). We reported the growth of high-quality and crack-free AlN film on sapphire substrate with a nanometer-scale-thick AlN nucleation layer (NL). Three kinds of nanometer-scale-thick AlN NLs, including in situ low-temperature AlN (LT-AlN) NL, oxygen-undoped ex situ sputtered AlN NL, and oxygen-doped ex situ sputtered AlN NL, were prepared for epitaxial growth of AlN films on sapphire substrates. The influence of nanoscale AlN NL thickness on the optical transmittance, strain state, surface morphology, and threading dislocation (TD) density of the grown AlN film on sapphire substrate were carefully investigated. The average optical transmittance of AlN film on sapphire substrate with oxygen-doped sputtered AlN NL was higher than that of AlN films on sapphire substrates with LT-AlN NL and oxygen-undoped sputtered AlN NL in the 200–270 nm wavelength region. However, the AlN film on sapphire substrate with oxygen-undoped sputtered AlN NL had the lowest TD density among AlN films on sapphire substrates. The AlN film on sapphire substrate with the optimum thickness of sputtered AlN NL showed weak tensile stress, a crack-free surface, and low TD density. Furthermore, a 270-nm AlGaN-based DUV LED was grown on the high-quality and crack-free AlN film. We believe that our results offer a promising and practical route for obtaining high-quality and crack-free AlN film for DUV LED.
Highlights
Aluminum gallium nitride (AlGaN)-based deep ultraviolet light-emitting diodes (DUV LEDs) have numerous applications, including sterilization, polymer curing, secure communication, and biochemical inspection [1,2,3,4,5]
For aluminum gallium nitride (AlGaN)-based DUV LEDs, aluminum nitride (AlN) film is usually used as the template for the epitaxial growth of the AlGaN layer due to its similar in-plane lattice constant and thermal expansion coefficient [6,7,8,9]
The AlGaN-based DUV LED was grown on AlN film on sapphire substrate with 25-nm-thick oxygen-undoped sputtered AlN nucleation layer (NL) by metal-organic chemical vapor deposition (MOCVD), including a 15-period
Summary
Aluminum gallium nitride (AlGaN)-based deep ultraviolet light-emitting diodes (DUV LEDs) have numerous applications, including sterilization, polymer curing, secure communication, and biochemical inspection [1,2,3,4,5]. For AlGaN-based DUV LEDs, aluminum nitride (AlN) film is usually used as the template for the epitaxial growth of the AlGaN layer due to its similar in-plane lattice constant and thermal expansion coefficient [6,7,8,9]. The characteristics of AlN film on sapphire substrate with different thicknesses of sputtered AlN NL is of significant interest for DUV LEDs. In this study, nanometer-scale-thick LT-AlN NL, oxygen-undoped sputtered AlN NL, and oxygen-doped sputtered AlN NL were prepared for the epitaxial growth of AlN films on sapphire substrates. The influence of nanoscale AlN NL thickness on the optical transmittance, strain state, surface morphology, and threading dislocation (TD) density of AlN film on sapphire substrate was investigated in detail. By optimizing AlN NL, we successfully grew a high-quality and crack-free AlN film on sapphire substrate and fabricated a 270-nm DUV LED
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