High performance inverted and large current double interface modulation-doped field-effect transistors with the bulk (Al,Ga)As replaced by superlattice at the inverted interface

Inverted modulation-doped field-effect transistors (MODFET’s) with 1-μm-long by 145-μm-wide gates and transconductances as high as 170 mS/mm have been demonstrated by replacing the troublesome doped bulk (Al,Ga)As with (Al,Ga)As/GaAs and AlAs/GaAs superlattices in which the dopants are incorporated only in the center of the GaAs wells. Mobilities of 4100 and 29 000 cm2/Vs and sheet carrier concentrations of 3.2×1012 and 1.3×1012 cm−2 at 300 and 77 K respectively were measured for superlattice inverted structures. In addition, double interface MODFET structures containing both normal and inverted heterointerfaces have been fabricated which demonstrate transconductances of 200 mS/mm and a saturation current as high as 340 mA/mm. This structure exhibited mobilities of 7200 and 54 000 cm2/Vs and sheet carrier concentrations 2.0×1012 and 1.6×1012 cm−2 at 300 and 77 K.