Electrical properties of shallow p⁺-n junction using boron-doped Si_1-xGe_x layer deposited by ultrahigh vacuum chemical molecular epitaxy

Strained boron-doped Si_1-xGe_x layers with different Ge mole fractions were selectively deposited by ultrahigh vacuum chemical molecular epitaxy to form shallow p⁺-n junction suitable for raised source/drain metal-oxide-semiconductor field effect transistor applications. Detailed electrical characterizations were performed. Our results show that the reverse leakage current could be optimized by a rapid thermal annealing at 950°C for 20 s, and a near perfect forward ideality factor (i.e., <1.01) is obtained for the p⁺-n Si_1-xGe_x/Si junction. By analyzing the periphery and area leakage current components of p⁺-n Si_1-xGe_x/Si junctions with various perimeter lengths and areas, the degree of misfit dislocations and undercut effect were studied. The specific contact resistance was found to decrease as Ge mole fraction increases. Junction depth measurements also show that the junction depth decreases monotonically with increasing Ge mole fraction. The reduced B diffusion constant is attributed to the increasing Ge gradient in the transition region.