Crystal Transformation of Cubic BN Nanoislands to Rhombohedral BN Sheets on AlN for Deep-UV Light-Emitting Diodes

The large bandgap and high p-type conductivity of sp(2)-bonded boron nitride (BN) make the compound very attractive for deep ultraviolet light-emitting diodes (DUV LEDs). However, integrating the promising sp(2) material in the DUV LED structure is challenging. This is because the reported growth conditions for scalable high-quality BN, including the high substrate temperature (>1300 degrees C) and the low-temperature (<1000 degrees C) buffer, can degrade the underneath Al-rich AlGaN quantum wells. Here, we demonstrate a wafer-scale sp(2)-bonded rhombohedral BN (rBN) attained on 2. AlN/sapphire substrates by metal-organic chemical vapor deposition (MOCVD), with a single growth temperature of 1180 degrees C. The multilayered BN stems from three-dimensional (3D) cubic BN (cBN) nanoislands self-assembled on AlN, which then spontaneously transform into continual rBN sheets. Evidenced by high-resolution transmission electron microscopy (HRTEM), the sharp BN/AlN interface is an important step toward next-generation DUV LEDs.