Plastic Relaxation of Highly Tensile Strained (100) Ge/InGaAs Heterostructures

Biaxial tensile strain has been shown to greatly enhance the optoelectronic properties of epitaxial germanium (Ge) layers. As a result, tensile-Ge (and#949t-Ge) layers grown on larger lattice constant InGaAs or GeSn have attracted great research interest. However, no previous studies have investigated the plastic relaxation occurring in these and#949t-Ge layers. Here, we experimentally demonstrate that plastic relaxation occurs in nearly all and#949t-Ge epitaxial layers that are of practical interest for optoelectronic applications, even when layers may still exhibit strain-enhanced characteristics. We show arrays of misfit dislocations (MDs), which are mostly disassociated, form at the and#949t-Ge/InGaAs interface for and#949t-Ge layers as thin as 15 nm with less than 1% total mismatch. Wedge geometry of plain view transmission electron microscopy (PV-TEM) foils is utilized to carry out a depth dependent investigation MD spacing for a range of and#949t-Ge/InGaAs heterostructures. MD spacing measured by PV-TEM is correlated to and#949t-Ge layer relaxation measured by high-resolution x-ray diffraction. We confirm very low relaxation (< 10% relaxed) in and#949t-Ge layers does not imply they have been coherently grown. We demonstrate plastic relaxation in the and#949t-Ge layer is acutely sensitive to grown-in threading dislocations (TDs) in the template material, and that reducing TD density is critical for maximizing strain retention. Given that and#949t-Ge layer thicknesses of 150+ nm with greater than 1% tensile strain are desired for optoelectronic devices, this work suggests that MDs may inevitably be present at and#949t-Ge/InGaAs heterointerfaces in practical devices, and that the effect of MDs on optoelectronic performance must be better understood.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Electrical Engineering

Department dc:contributor.department

Electrical and Computer Engineering

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2015

Author dc:creator

• Goley, Patrick Stephen

Chair dc:contributor.committeechair

• Hudait, Mantu K.

Committee members dc:contributor.committeemember

• Lester, Luke F.
• Heremans, Jean J.

• tensile
• strain
• germanium
• misfit dislocations
• stacking faults
• plastic relaxation
• elastic relaxation
• Shockley partial dislocations

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Dc Identifier Other

vt_gsexam:6044

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/54944