Transmission Electron Microscopy Study of the Structure of GaAs Layers in GaAs/Ge/GaAs Heterostructures

Heterostructures with an active region based on GaAs/Ge/GaAs layers are of interest for creating terahertz devices and topological insulators. The optical and electrical properties of such devices depend, to a great extent, on the conditions of their synthesis. In this work, the structure of GaAs layers in GaAs/Ge/GaAs heterostructures grown on a GaAs(001) substrate by molecular-beam epitaxy under process conditions providing a 90 degrees rotation of the crystal lattices of the upper and lower GaAs layers in samples of one type and no rotation in samples of the other type is examined. The synthesized heterostructures are studied by transmission electron microscopy and electron-diffraction analysis using thin cross-sectional foils prepared by the focused-ion-beam method. It is found that the GaAs/Ge/GaAs layers in samples of both types have a high crystal quality, but stacking faults and antiphase domains are formed in the GaAs layers located above the Ge layer. The relative orientation of the upper and lower GaAs layers in GaAs/Ge/GaAs is identified by comparing the intensity distributions in the disks 00 (2) over bar and 002 in the diffraction patterns obtained by convergent-beam electron diffraction. It is demonstrated by simulating the patterns that the orientation of the sample along the [310] zone axis is optimum for detecting differences between the diffraction patterns on pseudo-forbidden disks 00 (2) over bar and 002. The experimental diffraction patterns obtained under such conditions confirm the identical orientation of the crystal lattices of the upper and lower GaAs layers in samples of one type and the rotation of the lattices of these layers by 90 degrees about the [001] direction in the samples of the other type.