Impact on the microstructure, optical and electrical properties of cubic boron nitride thin films under post thermal annealing

High quality cubic boron nitride (c-BN) films are of importance for practical high power and high temperature device applications; however, the synthesis of c-BN films with high crystalline quality and desirable electrical properties remains challenging due to the poor adhesion and existence of the sp2-bonded interfacial layer. In this work, we demonstrate the impact of post-thermal annealing on the microstructure and electrical properties of interfacial layer in c-BN films. The spectral and high-resolution electron microscopic analysis reveals that in addition to the generally reported stress release, this post annealing causes a phase transition and re-orientation of sp(2)-BN interfacial layers. The studies on their optical and electrical properties reveal that the c-BN film annealed at 700 degrees C exhibits a maximal band gap of 5.90 eV and highest mobility of 15 cm(2)V(-1)s(-1) due to the phase transition and rearrangement of the interfacial layer. The c-BN/Si heterojunction after annealing shows rectifying performance at room temperature due to the presence of interfacial sp(2)-BN layer, where its defect levels and thickness play important roles on the carrier transport. This work provides additional insight on understanding and modulating the interface for the future applications of c-BN films in the fields of optics, optoelectronics, electrics. (C) 2022 Elsevier B.V. All rights reserved.