Evidence for Avalanche Operation in Sub-Micrometer Power GaN HEMTs with p-GaN Gate

We demonstrate the existence of sustainable avalanche operation on 100 V lateral- power GaN HEMT with submicrometer gate length. Results show that: (a) current-voltage I<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</inf>-V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</inf> measurements carried out as a function of device geometry demonstrate a significant and repeatable increase in drain current for voltages around 160 V (for the standard device geometry), corresponding to sustainable breakdown operation. Such phenomenon is only observed in “reference” pinch-off conditions (V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GS</inf>=0V), i.e. when a small sub-threshold current can flow through the devices. On the other hand (b), in “strong pinch-off” conditions (V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GS</inf>=-7 V), sustainable breakdown is not present, and devices reach a catastrophic failure (at higher voltage), due to the breakdown of the dielectric between field plate and drain. c) electroluminescence measurements indicate the presence of band-to-band luminescence, ascribed to the recombination of the holes generated by impact ionization (i.i.) with electrons near the source. d) temperature-dependent measurements indicate a positive temperature coefficient of the avalanche voltage.