Hydrogen-terminated diamond MESFETs: Operating principles, static and dynamic performance, and reliability

In this paper, we review the operating principles of hydrogen-terminated diamond MESFETs for high power and high frequency applications. Thanks to the transfer of electrons from the diamond valence band to the hydrogen termination a mobile hole channel is formed, leading to p-MOS operation. The resulting transistor shows good static performance, when the low technology readiness level of these devices is taken into account, owing to the excellent properties of diamond as a semiconductor. The dynamic performance is analyzed by means of quick ID-VD and ID-VG measurements carried out during a filling phase in off-state and on-state, and the corresponding recovery is monitored by the same measurements at different ambient temperatures. This measurement procedure allows for the extraction of the emission time constant and for the creation of the Arrhenius plot of the deep level involved, showing an activation energy of 0.30 eV. The short-term reliability of the devices is investigated by means of step-stress experiments in on-state condition. The degradation causes an increase in the on-resistance, a negative shift in the threshold voltage and a decrease in the peak transconductance value. The correlation between the variation in the electrical parameters and in the results of the dynamic characterization suggests that the degradation is caused by an increase in concentration of the aforementioned deep level, taking place both in the region below the gate and in the access region. A reduction in hole transfer efficiency can also be present, taking place at very high stress voltage.