We focused on investigation of the strain in GaAs/InGaAs and InGaAs/InAs bilayer microtubes by means of micro-Raman spectroscopy and comparison of the experimental results with calculated data.

The GaAs/In0.15Ga0.85As and In0.85Ga0.15As/InAs bilayer-based structures were grown by molecular beam epitaxy on GaAs and GaSb substrates, respectively. The GaAs/InGaAs bilayer is formed by 20nm thick In0.15Ga0.85As layer and GaAs top layer of 80 nm. GaAs/InGaAs bilayer consists of InAs layer (15nm) and In0.85Ga0.15As top layer (12nm).

A diameter of InGaAs/InAs microtubes was estimated as 3 mkm while for GaAs/InGaAs tube it was varied from about 20 to 3 mkm due to decreasing upper GaAs layer thickness in the wet etching process.

The micro-Raman scattering experiments were performed using different laser lines at 300K. The scattered light was analysed in backscattering geometry using a Dilor XY triple monochromator. Using a micro-Raman setup the incident laser light was focused with a spot size of 1 mm on a sample surface.

Through analysis of the frequencies of InAs- and GaAs phonon modes observed in the Raman spectra of mictrotubes and as-grown bilayers and comparison with numerical calculations the residual strain in mictrotubes was estimated. The overheating effects in the tubes were excluded by measuring Stokes-anti-Stokes ratio of the Raman-active modes and controlling microtube temperature. A depth profile of residual strain is tested by measuring Raman scattering excited with different laser lines for which the laser light has different penetration depths.

The numerical analysis was carried out using a commercial FE code, the ANSYS Academic Research product. The bilayer structure is modelled with 3-D 8-Node Solid Shell element. Roller and fixed boundary conditions are applied along the axis of symmetry and at the end of the structure, respectively.

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