Orientation Polarization Effect in Al$_{\text{2}}$O$_{\text{3}}$/Hydrogen-Terminated Diamond MISFETs

Drain current hysteresis phenomenon has been shown in hydrogen terminated diamond (H-diamond) metal-insulator-semiconductor field-effect transistors (MISFETs), in which the drain current varies with the sweep direction of the gate bias. This article aims to investigate the mechanism of this drain current hysteresis in the $\text{Al}_{\text{2}}{\text{O}}_{\text{3}}$ /H-diamond MISFETs. Firstly, the drain current at a direct current (dc) bias is measured with a 100 $\mu$ s sampling interval in 5 s. It is found that the dynamics of the drain current is opposite to that calculated using the trap model. Then, to reveal this anomalous phenomenon, an orientation polarization (OP) model accounting for adsorbates on the H-diamond surface is proposed. It shows that the relaxation induced by the orientational polarization results in a delay of the vertical electric field change in the channel under the gate, thus resulting in a drain current hysteresis at dc bias. The proposed model is verified by the combination of the measured gate capacitance versus frequency and the dynamic drain current measured at different biases and different temperatures. The activation energy calculated from the Arrhenius equation of the orientational polarization rather than traps is 0.0011 eV. The charging/discharging of the OP capacitance results in an overshoot of the drain current at the short pulse edges (PEs), which generates traps that lead to a drain current hysteresis at the pulse bias. The results of this article can be helpful for improving the reliability of H-diamond MISFETs.