BORON DELTA-DOPED SI AND GE0.2SI0.8 CHANNEL METAL-SEMICONDUCTOR FIELD-EFFECT TRANSISTORS GROWN BY MOLECULAR-BEAM EPITAXY

In this paper, we report the realization and the experimental investig ations of boron delta-doped Si- and Ge0.2Si0.8-Metal Semiconductor Fie ld-Effect Transistors (MESFET's) grown by molecular beam epitaxy (MBE) . Based on Hall measurements, a sheet carrier density of 5 X 1013 (1.8 X 1012) CM-2 and a carrier mobility of 34(120) cm2 . V-1 . s-1 for Ge 0.2Si0.8 (Si) 6-doped layer at 300 K were obtained. For the same devic e structure with an 5 mum Ag gate, the Si- and Ge0.2Si0.8-Channel MESF ET show an extrinsic transconductance of 0.56 mS/mm and 6.4 mS/mm, res pectively. The latter is much larger than that obtained previously in delta-doped Si MOSFETs reported in the literature. As compared to the Si-channel MESFET, the Ge0.2Si0.8 delta-FET (delta-FET) is shown havin g much smaller leakage current due to the band offset of the Si/Ge0.2S i0.8 heterointerface offering an excellent confinement for channel hol es, and much higher transconductance due to the Ge0.2Si0.8 channel pro mises a higher channel conductivity.