Strain-controlled Si-Ge modulation-doped FET with ultrahigh hole mobility

A novel modulation-doped field effect transistor (MODFET) with a strain-controlled Ge channel, p-Si/sub 0.5/Ge/sub 0.5//Ge/Si/sub 1-x/Ge/sub x/, is fabricated by molecular beam epitaxy (MBE). In order to enlarge the valence-band discontinuity, strain at the p-Si/sub 0.5/Ge/sub 0.5//Ge interface is controlled by changing the composition of the relaxed Si/sub 1-x/Ge/sub x/ layer. For this MODFET operated at around 77 K, an ultrahigh-field-effect mobility of approximately 9000 cm/sup 2//V-s is obtained.>