Diamond Schottky barrier diodes fabricated on sapphire-based freestanding heteroepitaxial diamond substrate

In this study, diamond Schottky barrier diodes (SBDs) fabricated on a sapphire-based heteroepitaxial diamond substrate were demonstrated. For commercializing diamond-based power electronics, a large-sized heteroepitaxial diamond substrate is essential. Sapphire is one of the most promising candidates among the diamond heteroepitaxial substrates because it can be produced on a large scale and its thermal expansion coefficient is similar to that of diamond, compared to that of any other non-diamond hetero substrate. The current-voltage characteristics of heteroepitaxial diamond SBDs grown under different growth rates were analyzed, and good rectification properties of SBDs were observed at the device grown with low growth rate. The ideality factor was 1.4, and the maximum breakdown field was approximately 1.1 MV/cm. The value of built-in potential derived from the capacitance-voltage characteristics was in good agreement with the approximated barrier heights. Some ball-shaped features on the SBD along the threading dislocation were directly observed after performing the breakdown test under reverse bias condition using transmission electron microscope (TEM). Threading dislocation which induces breakdown or large leakage current under reverse bias in diamond SBD was clarified and this will lead the research direction of a heteroepitaxial diamond electronic device. Recently, the diamond SBD grown on large-size heteroepitaxial diamond substrates becoming alternative to conventional high temperature high pressure (HPHT) diamond-based diamond SBD. In this study, diamond SBD grown on sapphire-based freestanding heteroepitaxial diamond substrate was successfully demonstrated. The sapphire substrate is one of the most promising material as substrate for heteroepitaxial diamond which is low cost and large sized. The heteroepitaxial diamond SBD structures with different growth rate were grown using microwave plasma CVD (MPCVD) and its structural properties were characterized. After device fabrication process, the detailed analysis of electrical properties of SBD were carried out. The direct observation of breakdown and leakage current features on SBD was obtained before and after electrical test under reverse bias condition.