Design rules for dislocation filters

TL;DR

This paper uses numerical modeling to evaluate the effectiveness of dislocation filter structures in reducing threading dislocation densities in epitaxial layers of various crystal structures, revealing exponential decay and material-specific behaviors.

Contribution

It provides new insights into the mechanisms and limits of threading dislocation reduction via filter structures in different crystal systems.

Findings

Dislocation densities decay exponentially with strain relief.

Reactions produce a balanced mixture of mobile and sessile dislocations in cubic materials.

Mobile dislocations are rapidly lost in GaN, with minimal impact on immobile dislocations.

Abstract

The efficacy of strained layer threading dislocation filter structures in single crystal epitaxial layers is evaluated using numerical modeling for (001) face-centred cubic materials, such as GaAs or Si(1-x)Ge(x), and (0001) hexagonal materials such as GaN. We find that threading dislocation densities decay exponentially as a function of the strain relieved, irrespective of the fraction of threading dislocations that are mobile. Reactions between threading dislocations tend to produce a population that is a balanced mixture of mobile and sessile in (001) cubic materials. In contrast, mobile threading dislocations tend to be lost very rapidly in (0001) GaN, often with little or no reduction in the immobile dislocation density. The capture radius for threading dislocation interactions is estimated to be approx. 40nm using cross section transmission electron microscopy of dislocation filtering structures in GaAs monolithically grown on Si. We find that the minimum threading dislocation density that can be obtained in any given structure is likely to be limited by kinetic effects to approx. 1.0e+04 to 1.0e+05 per square cm.