Defects in Device Grade Homoepitaxial Diamond Thin Films Grown with Ultra-Low CH4/H2 Conditions by Microwave-Plasma Chemical Vapor Deposition

Recent progress in our study of high-quality homoepitaxial diamond thin film growth was achieved thanks to a low CH4/H2 ratio used during microwave-plasma chemical vapor deposition (CVD). Deposited films showed atomically flat surfaces and excitonic emission (5.27 eV) at room temperature, while band-A emission (2.95 eV) originating from defect-related centers was decreased. Using these films, we have also realized excellent properties of Schottky junctions between Al and the high-conductivity layer near the hydrogenated surface, indicating that these films are device grade ones. On the other hand, when the CH4 concentration was increased, homoepitaxial diamond films contained unepitaxial crystallites (UC), which degraded the Schottky junction properties. Other parts of the top flat surface showed excitonic emission at room temperature, indicating that this region is still of the device grade quality. We found that the band-A emission only appeared at UC sites. High-resolution transmission electron microscopy (HRTEM) revealed that many amounts of (111) Σ3 twin boundaries and some defects around them existed.