Anomalous behavior of AlGaN/GaN heterostructure field-effect transistors at cryogenic temperatures: From current collapse to current enhancement with cooling

While current collapse affects AlGaN/GaN heterojunction field-effect transistors (HFETs) around room temperature, it gradually gives place to a current enhancement with cooling—below 200 K, electrically stressed devices do show higher currents than in their prestressed state. This behavior can be explained by increased levels of channel impact ionization at lower temperatures. The positive hole charge generated by impact ionization compensates (and eventually dominates) the parasitic negative charge that is responsible for current collapse at higher temperatures (i.e., the “virtual gate charge”). Cooling of AlGaN/GaN HFETs may potentially alleviate some of the nonidealities that have so far plagued this technology.