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

Abstract

Using nitrogen-dioxide (NO2) adsorption treatment and Al2O3 passivation technique, we improved drain current (IDS) of hydrogen-terminated (H-terminated) diamond field-effect transistors (FETs). The Al2O3 passivation layer also serves as a gate-insulator in a gate region. Maximum IDS (IDSmax) of -1.35 A/mm was obtained for the diamond FETs with NO2 adsorption and the Al2O3 passivation layer. This IDSmax is the highest ever reported for diamond FETs and indicates that the Al2O3 passivation layer can stabilize adsorbed NO2, which increases the hole carrier concentration on the H-terminated diamond surface. In RF small-signal characteristics, the diamond FETs with NO2 adsorption and the Al2O3 passivation layer showed high cutoff-frequency (fT) and maximum frequency of oscillation (fmax) in a wide gate–source voltage (VGS) range (>10 V). This is because the Al2O3 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.