In-plane strain distribution in free-standing GaAs/InGaAs/GaAs single quantum well surface nanostructures on GaAs[001]

The vertical variation of in-plane strain induced by an In0.1Ga0.9As single quantum well (SQW) embedded in a free-standing wire structure on GaAs[001] has been investigated by depth resolved x-ray grazing incidence diffractio n. If the wires are oriented along the [110] direction both the shape and s train influence on the x-ray intensity distribution can be separated by run ning transverse or longitudinal scans across the grating truncation rods (G TRs) close to the ((2) over bar 20) and ((2) over bar (2) over bar 0) in-pl ane Bragg reflection, respectively. The GTRs themselves are modulated due t o the vertical layering of the wires. The vertical strain variation in the vicinity of SQW is particularly inspected at the weak (200) Bragg reflectio n which is most sensitive to the scattering density difference between the SQW and GaAs. The theoretical analysis is based on the distorted wave Born approximation for grazing incidence geometry. The structural parameters of the surface nanostructure were determined with high accuracy by fitting of the complete set of experimental GTRs simultaneously. In agreement with fin ite-element calculations we find a maximum in-plane lattice displacement wi thin the SQW of (Delta a(parallel to)/a approximate to 3.5X10(-4)) with res pect to the substrate. It induces dilative in-plane strain in the GaAs conf inement layers decreasing towards the upper free surface and the bulk, resp ectively. The evaluated in-plane strain within the SQW is used for estimati ng the strain induced redshift of the photoluminescence wavelength of the r espective optical device. (C) 1999 American Institute of Physics. [S0021-89 79(99)07503-9].