Structural characterisation of a GaAs surface wire structure by triple axis X-ray grazing incidence diffraction

The triple-axis equipment under X-ray grazing incidence diffraction was applied for the first time in order to realise high-resolution investigations of the morphology and the strain state in a free-standing lateral nanostructure on GaAs [001]. Because the defined wires containing a thin GaInAs single quantum well (SQW) are aligned along [1(1) over bar 0] we were able to determine the wire shape and their strain profile separately running either angular or radial scans across the (220) and (2(2) over bar 0) in-plane Bragg reflection. Assuming a trapezoedric shape, the inclination of the wire side walls and the etching depth became available running rod scans at different angular positions of the grating side peaks. All these information were obtained from different depths below the surface. The thickness of the GaAs layer covering the buried SQW was determined at the weak (200) reflection. For this particular sample we determined the lateral spacing D = (320 +/- 4) nm and the etching depth t(e), = (54 +/- 2) nm from reciprocal space maps within the (q[220], q[001]) plane. The wire side walls are inclined by an angle gamma=18 degrees with respect to the surface. The 5nm thick GaInAs SQW buried under a t(cap) = (20 +/- 2)nm thick GaAs cover layer induces dilatative strain mainly on top but rather compressive strain at the bottom of the wires. (C) 1998 Elsevier Science B.V. All rights reserved.