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 investigations of boron δ-doped Si- and Ge_0.2Si_0.8-Metal Semiconductor Field-Effect Transistors (MESFET’s) grown by molecular beam epitaxy (MBE). Based on Hall measurements, a sheet carrier density of 5× 10¹³ (1.8× 10¹²) cm^-2 and a carrier mobility of 34(120) cm²\cdotV^-1\cdots^-1 for Ge_0.2Si_0.8 (Si) δ-doped layer at 300 K were obtained. For the same device structure with an 5 μm Ag gate, the Si- and Ge_0.2Si_0.8-channel MESFET show an extrinsic transconductance of 0.56 mS/mm and 6.4 mS/mm, respectively. 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 Ge_0.2Si_0.8 delta-FET (δ-FET) is shown having much smaller leakage current due to the band offset of the Si/Ge_0.2Si_0.8 heterointerface offering an excellent confinement for channel holes, and much higher transconductance due to the Ge_0.2Si_0.8 channel promises a higher channel conductivity.