Atomic-Layer Doping in Si1-xGex/Si/Si1-xGex Heterostructures by Two-Step Solid-Phase Epitaxy

A two-step solid-phase epitaxy (SPE) technique was developed to solve the problem of Sb segregation during the growth of Si1-x Ge x /Si/Si1-x Ge x heterostructures with Sb atomic-layer doping. At below 100°C Sb was deposited onto the Si1-x Ge x layer crystallized in the first SPE process to eliminate the diffusion of Sb during the second SPE process to form the Si1-x Ge x layer on the Sb layer. As a result, a sharp Sb depth profile and high electrical activation in the Sb-doped Si1-x Ge x layer was obtained. However, the number of modulation-doped carriers in the Si channel layer was small. Calculation of the carrier distribution between the channel and the doped layer suggested that the carrier density in the channel was low when the Sb-doping profile was sharp, thus precise control of the modulation-doped-carrier density by optimizing the thickness of the Sb-doped layer is crucial for fabricating modulation-doped field-effect transistors.