Anomalous Kink Effect in GaN High Electron Mobility Transistors

Abstract

An anomalous kink effect has been observed in the room-temperature drain current <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ID</i> versus drain voltage <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> characteristics of GaN high electron mobility transistors. The kink is originated by a buildup (at low <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> ) and subsequent release (at high <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> ) of negative charge, resulting in a shift of pinch-off voltage <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">VP</i> toward more negative voltages and in a sudden increase in <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ID</i> . The kink is characterized by extremely long negative charge buildup times and by a nonmonotonic behavior as a function of photon energy under illumination. The presence of traps in the GaN buffer may explain both spectrally resolved photostimulation data and the slow negative charge buildup.