Normally-Off Thin-Film Silicon Heterojunction Field-Effect Transistors and Application to Complementary Circuits

A thin blocking structure is incorporated in the gate-stack of heterojunction field-effect transistor (HJFET) devices to substantially suppress the gate current when the gate heterojunction is forward-biased. As a result, normally-OFF HJFET devices with MOSFET-like characteristics are obtained. The HJFET devices are comprised of gate, source, and drain regions formed by plasma-enhanced chemical vapor deposition on thin-film crystalline Si substrates at temperatures below 200°C. The ON/OFF ratios larger than 106, operation voltages as low as 1 V, and subthreshold slopes of ~85 mV/decade are demonstrated. The HJFET devices can be integrated with MOSFET devices fabricated on the same crystalline Si substrates to form complementary circuits.