Fast growth of crack-free thick AlN film on sputtered AlN/sapphire by introducing high-density nano-voids

Abstract

Recently, there have been increasing demands for high-quality AlN/sapphire templates due to their applications in deep ultraviolet light-emitting diodes (DUV LEDs). To acquire a low threading dislocation density (TDD), AlN films are usually thickened to promote dislocation interaction. However, micro cracks are easily generated when their thicknesses exceed 2–3 μm, severely deteriorating device performances. In this study, we successfully fabricated a 5.6 μm-thick crack-free AlN film by employing a medium-temperature (MT) interlayer. It is revealed that high-density (1.7 × 1010 cm−2) nano-voids were self-organized above the MT interlayer, which effectively destroyed the coherence between the MT interlayer and the subsequent epilayer by reducing contact area. As a result, tensile stress in the AlN film during growth was significantly decreased to 0.18 GPa, demonstrating a 64% reduction compared with its counterpart without nano-voids. In addition, the thick AlN film with embeded nano-voids allowed dislocations to climb long distances for mutual annihilation, so the TDD of the AlN film was significantly decreased to an extremely low value of 4.7 × 107 cm−2. This technique paves the way for achieving high-performance DUV LEDs and other optoelectronic/electronic devices.