ENHANCEMENT MODE N-CHANNEL SI/SIGE MODFET WITH HIGH INTRINSIC TRANSCONDUCTANCE

n-channel Si/SiGe MODFETs with quantum wells grown on a thick (1.5-mu-m) graded buffer (Ge 5-30%) are realised. MODFETs with a surface gate work in the depletion mode due to a large gate-to-2-DEG channel distance of 75 nm. MODFETs with a recessed gate 10-15 nm above the channel exhibit enhancement mode operation with significantly high extrinsic transconductances of 340 mS/mm or 670 mS/mm at 300 K or 77 K and corresponding intrinsic transconductances of 380 mS/mm or 800 mS/mm. The performance indicates the improved layer quality on graded buffers.