Strain commonly observed in layers grown by epitaxial lateral overgrowth (ELO) and arising from interaction of the layers with the mask underneath is studied. We show that GaAs ELO layers grown by liquid-phase epitaxy on SiO2-coated GaAs substrates are strain free if the laterally overgrown parts (“wings”) of the layers hang over and have no direct contact with the mask. In other cases, tilting of the wings can be efficiently tailored by controlling the ratio of vertical to lateral growth rates at the beginning of ELO growth. In particular, this has been achieved by growing GaAs ELO layers on SiO2-coated GaAs substrates with increasing density of dislocations. Then, the ratio of vertical to lateral growth rates at the beginning of the growth is increased which in turn leads to reduction of the adhesion-induced bending of the ELO wings, as we observe by high-resolution x-ray diffraction. In the limiting case of heavily dislocated substrates, namely, on GaAs-coated Si, the vertical growth of GaAs ELO is so fast that air-bridged structures without any wing adhesion to the SiO2 mask are obtained. Next, the same model is used to explain our earlier data on negligible bending of GaAs ELO layers on graphite-masked GaAs substrates. In this case, delayed start of lateral growth is caused by the change of the shape of the melt in the corner between the sidewall of the ELO layer and the mask when SiO2 was replaced by graphite film not wetted by the gallium melt.
High resolution x-ray diffraction has been used to study strain in GaAs layers grown on GaAs substrates by the liquid phase epitaxial lateral overgrowth (ELO) technique. We show that the lattice and thermal expansion coefficient mismatch between the subsequent layers and the substrate, as well as the built-in strain in the SiO2 masking film, lead to long-range deformations (macroscopic bending) extending over the whole area of the sample. Moreover, we show evidences that microscopic bending of individual ELO stripes takes place due to adhesion of their laterally overgrown parts to the masking film.
X-ray diffraction has been used to study the influence of the mask material on properties of GaAs layers grown by the liquid phase epitaxial lateral overgrowth (ELO) on (100) GaAs substrates. We show that ELO stripes bend towards the SiO2 mask in the direction perpendicular to seeding lines in a similar way to that as studied recently by x-ray topography for Si lamellae [H. Raidt, R. Kohler, F. Banhart, B. Jenichen, A. Gutjahr, M. Konuma, I. Silier, and E. Bauser, J. Appl. Phys. 80, 4101 (1996)]. The bending disappears when the mask is removed by selective etching. This microscopic bending is reduced by nearly 2 orders of magnitude when graphite instead of SiO2 is used to mask the substrate.
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