High-reliability passivation of hydrogen-terminated diamond surface by atomic layer deposition of Al₂O₃

Although the two-dimensional hole gas (2DHG) of a hydrogen-terminated diamond surface provides a unique p-type conducting layer for high-performance transistors, the conductivity is highly sensitive to its environment. Therefore, the surface must be passivated to preserve the 2DHG, especially at high temperature. We passivated the surface at high temperature (450°C) without the loss of C-H surface bonds by atomic layer deposition (ALD) and investigated the thermal reliability of the Al₂O₃ film. As a result, C-H bonds were preserved, and the hole accumulation effect appeared after the Al₂O₃ deposition by ALD with H₂O as an oxidant. The sheet resistivity and hole density were almost constant between room temperature and 500°C by the passivation with thick Al₂O ₃ film thicker than 38nm deposited by ALD at 450°C. After the annealing at 550°C in air The sheet resistivity and hole density were preserved. These results indicate the possibility of high-temperature application of the C-H surface diamond device in air. In the case of lower deposition temperatures, the sheet resistivity increased after air annealing, suggesting an insufficient protection capability of these films. Given the result of sheet resistivity after annealing, the increase in the sheet resistivity of these samples was not greatly significant. However, bubble like patterns were observed in the Al₂O₃ films formed from 200 to 400°C by air annealing at 550°C for 1 h. On the other hand, the patterns were no longer observed at 450°C deposition. Thus, this 450°C deposition is the sole solution to enabling power device application, which requires high reliability at high temperatures.