Diamond field-effect transistors with 1.3A/mm drain current density by Al ₂O ₃ passivation layer

Using nitrogen-dioxide (NO ₂) adsorption treatment and Al ₂O ₃ passivation technique, we improved drain current (IDS) of hydrogen-terminated (Hterminated) diamond field-effect transistors (FETs). The Al ₂O ₃ passivation layer also serves as a gate-insulator in a gate region. Maximum IDS (I _DSmax) of -1:35A/mm was obtained for the diamond FETs with NO ₂ adsorption and the Al ₂O ₃ passivation layer. This I _DSmax is the highest ever reported for diamond FETs and indicates that the Al ₂O ₃ passivation layer can stabilize adsorbed NO ₂, which increases the hole carrier concentration on the H-terminated diamond surface. In RF small-signal characteristics, the diamond FETs with NO ₂ adsorption and the Al ₂O ₃ passivation layer showed high cutoff-frequency (fT) and maximum frequency of oscillation (f _max) in a wide gate-source voltage (VGS) range (>10 V). This is because the Al ₂O ₃ gate insulator with a high potential barrier against hole carriers can confine and control the high concentration of hole carriers and then high forward-bias voltage can be applied without noticeable gate leakage current.