THE EFFECT OF IN-SITU BORON DOPING ON THE STRAIN RELAXATION OF SI0.8GE0.2-B/SI HETEROSTRUCTURE GROWN BY MOLECULAR-BEAM EPITAXY

Abstract

The effect of in situ elemental boron doping (boron concentration N-B = 1 x 10(19) to 3 X 10(20) cm(-3)) on the strain relaxation of a Si0.8Ge0.2:B/Si(001) heterostructure grown at 680 degrees C is investigated. Although boron gives rise to lattice contraction in bulk Si, it does not compensate the lattice mismatch between the Si0.8Ge0.2 layer and Si substrate. On the contrary, it stimulates the strain relaxation. The strain relaxation of the Si1-xGex:B/Si(001) heterostructure mainly gives way to dislocation half-loops generated not in the Si0.8Ge0.2 layer, but in the Si buffer layer just below it. This means that heterointerfacial quality may be one of the major control factors of strain relaxation. The strain relaxation induced by boron doping is observed even at N-B similar to 10(19) cm(-3), which is in the doping range typically used in Si1-xGex/Si heterojunction bipolar transistors (HBTs). Therefore, as well as Ge mole fraction and growth temperature, N-B should also be considered in determining critical thickness of a Si1-xGex layer grown on a Si substrate.