Burgers Vector Analysis of Vertical Dislocations in Ge Crystals by Large-Angle Convergent Beam Electron Diffraction.
By transmission electron microscopy with extended Burgers vector analyses, we demonstrate the edge and screw character of vertical dislocations (VDs) in novel SiGe heterostructures. The investigated pillar-shaped Ge epilayers on prepatterned Si(001) substrates are an attempt to avoid the high defect densities of lattice mismatched heteroepitaxy. The Ge pillars are almost completely strain-relaxed and essentially defect-free, except for the rather unexpected VDs. We investigated both pillar-shaped and unstructured Ge epilayers grown either by molecular beam epitaxy or by chemical vapor deposition to derive a general picture of the underlying dislocation mechanisms. For the Burgers vector analysis we used a combination of dark field imaging and large-angle convergent beam electron diffraction (LACBED). With LACBED simulations we identify ideally suited zeroth and second order Laue zone Bragg lines for an unambiguous determination of the three-dimensional Burgers vectors. By analyzing dislocation reactions we confirm the origin of the observed types of VDs, which can be efficiently distinguished by LACBED. The screw type VDs are formed by a reaction of perfect 60° dislocations, whereas the edge types are sessile dislocations that can be formed by cross-slips and climbing processes. The understanding of these origins allows us to suggest strategies to avoid VDs.
1Institute of Semiconductor and Solid State Physics,Johannes Kepler University Linz,Altenbergerstr. 69,4040 Linz,Austria.
Heiko
H
Groiss
1Institute of Semiconductor and Solid State Physics,Johannes Kepler University Linz,Altenbergerstr. 69,4040 Linz,Austria.
Martin
M
Glaser
2L-NESS and Department of Materials Science,Università degli Studi di Milano-Bicocca,via Cozzi 53,20125 Milano,Italy.
Anna
A
Marzegalli
3L-NESS and Department of Physics,Politecnico di Milano,via Anzani 42,22100 Como,Italy.
Fabio
F
Isa
3L-NESS and Department of Physics,Politecnico di Milano,via Anzani 42,22100 Como,Italy.
Giovanni
G
Isella
2L-NESS and Department of Materials Science,Università degli Studi di Milano-Bicocca,via Cozzi 53,20125 Milano,Italy.
Leo
L
Miglio
1Institute of Semiconductor and Solid State Physics,Johannes Kepler University Linz,Altenbergerstr. 69,4040 Linz,Austria.
Friedrich
F
Schäffler
SiGe; burgers vector analysis; dislocations; large-angle convergent beam electron diffraction; transmission electron microscopy