Fixed charges investigation in Al2O3/hydrogenated-diamond metal-oxide-semiconductor capacitors

Electrical properties of Al2O3/hydrogenated-diamond (H-diamond) metal-oxide-semiconductor (MOS) capacitors are investigated and discussed in this study. Al2O3 gate dielectrics are deposited at 120, 200, and 300 °C by an atomic layer deposition technique. For the H-diamond MOS capacitors with Al2O3 deposited at 120, 200, and 300 °C, leakage current densities at an electric field of 3.0 MV cm−1 are 8.4 × 10−4, 7.1 × 10−6, and 7.5 × 10−5 A cm−2, respectively. A small decrease in the maximum capacitance of the Al2O3 (120 °C)/H-diamond MOS capacitor is observed when the measurement frequency is increased from 1 kHz to 100 kHz. However, the maximum capacitances of the Al2O3 (200 °C)/H-diamond and Al2O3 (300 °C)/H-diamond MOS capacitors are stable. Experimental flatband voltage in the capacitance–voltage curve of the Al2O3 (120 °C)/H-diamond MOS capacitor shifts to the left with respect to theoretical flatband voltage. However, they shift to the right for the Al2O3 (200 °C)/H-diamond and Al2O3 (300 °C)/H-diamond MOS capacitors. Therefore, when the deposition temperature of Al2O3 is increased from 120 to 300 °C, polarity of the fixed charges in the H-diamond MOS capacitors changes from positive to negative. This phenomenon is explained by the variations of negatively charged acceptors at the Al2O3/H-diamond interface and oxygen vacancies in the Al2O3 film.