HIGH-TRANSCONDUCTANCE N-TYPE SI/SIGE MODULATION-DOPED FIELD-EFFECT TRANSISTORS

We 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 employing ultrahigh vacuum/chemical vapor deposition (UHV/CVD), the mobility and electron sheet charge density in the strained Si channel are 1500 (9500) CM2/V.s and 2.5 x 10(12) (1.5 x 10(12)) cm-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 MESFET's and are comparable to the best results achieved in GaAs/AlGaAs modulation-doped transistors.