Studies of boron diffusivity in strained Si1−xGex epitaxial layers

Abstract

Diffusion of boron in compressively strained Si1−xGex alloy layers grown by rapid pressure chemical vapor deposition has been studied as a function of Ge fractions for 0.0006⩽x⩽0.15 and annealing temperature. The comparison of the Si1−xGex samples to the Si samples after rapid thermal and furnace anneals revealed a retarded B diffusion inside the strained Si1−xGex epitaxial layers. The influence of the Ge content on the dopant diffusion was also measured and simulated, demonstrating that the diffusion of B and the extracted bang-gap change was found to decrease with the Ge alloy content, and the extracted activation energies for diffusion were found to increase with increasing Ge content in the investigated composition range. The influence of various factors on the B diffusivity is studied and their importance is discussed elaborately. A simple empirical expression for the B retardation is presented and incorporated into a diffusion model for dopants in heterostructures. Good agreement between the measured and simulated diffusivity that includes the model for strain and chemical effects is obtained.