Recessed-gate GaN-based MIS-HEMTs Performance Dependence on Recess Depth

We studied the electrical performance of recessed-gate GaN-based MIS-HEMTs, particularly the non-monotonic dependence of transconductance g<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> on recess depth of the AlGaN barrier in the channel region. From planar structure with original AlGaN barrier thickness in the channel (d<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CH</inf>) of 25 nm, reducing d<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CH</inf> to 15 nm by dry-etching, threshold voltage (V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</inf>) shift positively while the maximum transconductance g<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m,max</inf> increased. However, when the d<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CH</inf> was further reduced to 6 nm, while V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</inf> still shifted towards positive voltage direction, g<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m.max</inf> was significantly decreased. Our results suggest that for a given MIS-HEMT structure, there is an optimum recess depth that will result in the highest g<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m.max</inf>. Our findings could provide important guidelines for achieving optimal performance from normally-off recessed-gate GaN-based MIS-HEMTs designed using interface charge engineering.