Method for forming low defect density alloy graded layers and structure containing such layers

[0034] This invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,”“comprising,” or “having,”“containing,”“involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

[0035] In the past, some methods to further reduce threading dislocation density in alloy graded layers have called for undesirable modifications that impose undue limitations on the structure. For example, in the case of silicon germanium, one technique requires that the relaxed silicon germanium graded layer is doped with antimony concentrations greater than ab