High-transconductance n-type Si/SiGe modulation-doped field-effect transistors

The authors report on the fabrication and the resultant device characteristics of the first 0.25- mu m gate-length field-effect transistor based on n-type modulation-doped Si/SiGe. Prepared using ultrahigh vacuum/chemical vapor deposition (UHV/CVD), the mobility and electron sheet charge density in the strained Si channel are 1500 (9500) cm/sup 2//V-s and 2.5*10/sup 12/ (1.5*10/sup 12/) cm/sup -2/ at 300 K (77 K). At 77 K, the devices have a current and transconductance of 325 mA/mm and 600 mS/mm, respectively. These values far exceed those found in Si MESFETs and are comparable to the best results achieved in GaAs/AlGaAs modulation-doped transistors.>