Suppression of Anomalously Large Threshold Voltage in Wafer-Bonded Vertical Transistors by Enhancing Critical Field to Impact Ionization

Impact ionization has been seen to effect pinchoff in wafer-bonded aperture vertical electron transistors (BAVETs) comprising an InGaAs channelwafer-bonded to a III-nitride (III-N) drift region. The InGaAs-III-N junction is referred to as thewafer-bondedinterface (WBI). Field plating can work well to manage the peak field and related impact ionization; however, it comeswith a tradeoffof increasedonresistance. In this paper, another control knob to breakdown is explored in the critical field (xi CRIT_ IMPCT) of a BAVET. Investigation focuses on the characteristics of devices that differ in their InAlAs doping profile, namely p-type, unintentional, or a combination of both. These devices are tested for the role of field plate, built-in voltage, and trap behavior on pinchoff. It is shown that the change of doping causes a dramatic change to the trap activity at WBI. These traps ionize and determine xi CRIT_ IMPCT as ionization of traps that leads to an early onset of impact ionization in the channel, which weakens pinchoff in a BAVET. Passivating traps is proposed to be amethod to improvingpinchoff. Trap passivation ofWBI is demonstrated if InAlAs is dopedp-type rather than unintentionally. A consequent enhancement in pinchoff and breakdownvoltageof aBAVET is also reported.