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-μm 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 1012 (1.5 x 1012) 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. © 1992 IEEE