Coalescence induced dislocation reduction in selectively grown lattice-mismatched heteroepitaxy: Theoretical prediction and experimental verification

Abstract

A method for reduction of threading dislocation density (TDD) in lattice-mismatched heteroepitaxy is proposed, and the reduction is experimentally verified for Ge on Si. Flat-top epitaxial layers are formed through coalescences of non-planar selectively grown epitaxial layers, and enable the TDD reduction in terms of image force. Numerical calculations and experiments for Ge on Si verify the TDD reduction by this method. The method should be applicable to not only Ge on Si but also other lattice-mismatched heteroepitaxy such as III-V on Si.

Reduced threading dislocation density in a germanium epitaxial film coalesced on an arrayed silicon-on-insulator strip

“…The void formation, derived from no Ge deposition on the SiO 2 surface, is similar to our previous study on a selective growth of Ge on Si covered with an array of SiO 2 strip masks. 42,43) The difference between the flat surface for the 0.3 and 0.5 μm wide strips and the faceted surface for the 1.5 μm wide strip is probably related to the Ge 095506-2…”

“…In this growth condition, a pure Ge film uniform in thickness has been grown directly on an unpatterned (001) Si/SOI surface. [42][43][44][45][46][47] The background hole concentration in an undoped Ge film was approximately 1 × 10 16 cm −3 , according to the Hall-effect measurement, realizing a high-performance pin photodiode. 14,16,17,[19][20][21] The thickness of Ge was designed to be 1000 nm on an unpatterned flat surface.…”

“…A similar downward bending of a dislocation has been observed in our previous study on a coalesced Ge layer on Si with an SiO 2 mask array. 42,43) The downward bending has been ascribed to the effect of an image force acting on the dislocation toward the free surface, i.e. the void surface.…”

“…42) As an alternative approach, our group has proposed a method utilizing a coalescence of adjacent Ge strips selectively grown on Si covered with an arrayed SiO 2 mask. 42,43) Semicylindrical voids are embedded in the coalesced Ge film over the SiO 2 masks, bending the dislocations in Ge downward to the void surface. An image force acting on the dislocation, which is an attractive force toward the free surface, is responsible for this downward bending.…”

“…A termination of the dislocation at the void surface leads to a TDD reduction, as experimentally verified by an etch-pit density (EPD) measurement. 42,43) In this work, the coalescence method is applied to a Si-oninsulator (SOI) wafer, which is a standard platform in Si photonics. Instead of an arrayed growth mask of submicron SiO 2 strips in Refs.…”