Reduced Threading Dislocation Density in a Ge Epitaxial Film on a Submicron-Patterned Si Substrate Grown by Chemical Vapor Deposition

A patterned Si substrate is used to reduce the threading dislocation density (TDD) in a Ge epitaxial film for near-infrared photonic device applications. Using photolithography and dry etching, an array of submicron-wide strips with a rectangular cross-section is patterned in the [110] direction of a Si (001) wafer. A Ge film as thick as 1 mu m is grown on the patterned Si by chemical vapor deposition with an ordinary two-step growth method, where a buffer layer of pure Ge as thin as 50 nm is grown at a low temperature of 370 degrees C, followed by growth at an elevated temperature of 700 degrees C. A Ge film is formed with a reasonably flat surface despite the non-flat starting Si surface as well as the large lattice mismatch of 4.2% between Ge and Si. The etch-pit density measurements for the Ge film exhibits TDD of about 6 x 10(7) cm(-2), which is significantly lower than that of about 2 x 10(8) cm(-2) for the film on the unpatterned region prepared on the same Si substrate. The TDD reduction is attributed to a trapping of the dislocations in the trench regions between the Si strips, as observed in cross-sectional transmission electron microscope images.

Automated summary

A patterned Si substrate is used to reduce the threading dislocation density in a Ge epitaxial film. The Ge film is grown on the patterned Si using chemical vapor deposition with a two-step growth method. The trapping of dislocations in the trench regions between the Si strips contributes to the TDD reduction in the Ge film.