STRUCTURAL CHARACTERIZATION OF A GAAS SURFACE WIRE STRUCTURE BY TRIPLE AXIS X-RAY GRAZING-INCIDENCE DIFFRACTION

The triple-axis equipment under X-ray grazing incidence diffraction wa s applied for the first time in order to realise high-resolution inves tigations of the morphology and the strain state in a free-standing la teral nanostructure on GaAs [001]. Because the defined wires containin g 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 prof ile separately running either angular or radial scans across the (220) and (2(2) over bar 0) in-plane Bragg reflection. Assuming a trapezoed ric shape, the inclination of the wire side walls and the etching dept h became available running rod scans at different angular positions of the grating side peaks. All these information were obtained from diff erent depths below the surface. The thickness of the GaAs layer coveri ng the buried SQW was determined at the weak (200) reflection. For thi s particular sample we determined the lateral spacing D = (320 +/- 4) nm and the etching depth t(e), = (54 +/- 2) nm from reciprocal space m aps within the (q[220], q[001]) plane. The wire side walls are incline d by an angle gamma=18 degrees with respect to the surface. The 5nm th ick GaInAs SQW buried under a t(cap) = (20 +/- 2)nm thick GaAs cover l ayer induces dilatative strain mainly on top but rather compressive st rain at the bottom of the wires. (C) 1998 Elsevier Science B.V. All ri ghts reserved.