Diamond Field-Effect Transistors with 1.3 A/mm Drain Current Density by Al₂O₃ Passivation Layer

Abstract

Using nitrogen-dioxide (NO 2 ) adsorption treatment and Al 2 O 3 passivation technique, we improved drain current ( I DS ) of hydrogen-terminated (H-terminated) diamond field-effect transistors (FETs). The Al 2 O 3 passivation layer also serves as a gate-insulator in a gate region. Maximum I DS ( I DSmax ) of -1.35 A/mm was obtained for the diamond FETs with NO 2 adsorption and the Al 2 O 3 passivation layer. This I DSmax is the highest ever reported for diamond FETs and indicates that the Al 2 O 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 2 O 3 passivation layer showed high cutoff-frequency ( f T ) and maximum frequency of oscillation ( f max ) in a wide gate–source voltage ( V GS ) range (>10 V). This is because the Al 2 O 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.