Effect of helium ion implantation and annealing on the relaxation behavior of pseudomorphic Si1-xGex buffer layers on Si (100) substrates

The influence of He implantation and annealing on the relaxation of Si0.7Ge0.3 layers on Si (100) substrates is investigated. Proper choice of the implantation energy results in a narrow defect band approximate to100 nm underneath the substrate/epilayer interface. During annealing at 700-1000 degreesC, He-filled bubbles are created, which act as sources for misfit dislocations. Efficient annihilation of the threading dislocations is theoretically predicted, if a certain He bubble density with respect to the buffer layer thickness is maintained. The variation of the implantation dose and the annealing conditions changes density and size of spherical He bubbles, resulting in characteristic differences of the dislocation structure. Si1-xGex layers with Ge fractions up to 30 at. % relax the initial strain by 70% at an implantation dose of 2x10(16) cm(-2) and an annealing temperature as low as 850 degreesC. Simultaneously, a low threading dislocation density of 10(7) cm(-2) is achieved. The strain relaxation mechanism in the presence of He filled bubbles is discussed. (C) 2002 American Institute of Physics.