Investigation of insulated buried layers obtained by ion implantation in AlGaAs with various Al concentration

The important element of modern Al_xGa_1-xAs semiconductor lasers is an insulating buried layer introduced by selective implantation with He or H ions. The difficulty in obtaining of such layers is connected with controlling of strain and defects introduced by implantation, which may disturb the action of the laser. The strain may be however controlled in less complicated laterally homogeneous structures or even single implanted layer.
The insulated buried layers obtained by implantation of 150 keV He ions to Al_xGa_1-xAs with various concentration of Al and GaAs were studies with different synchrotron diffraction methods exploring both white and monochromatic beam.The selected samples were studied with high resolution transmission electron microscopy. The implantation were performed at room temperature, 80°C and 120°C. The doses were in the range from 2x10¹⁶ to 6x10¹⁶ cm^-2. The synchrotron experiment included taking local rocking curves using small 50x50 µm² probe beam. The rocking curves exhibit characteristic sequence of interference maxima and enabled the analysis of the strain profiles by fitting the theoretical rocking curves obtained by numerical integration of the Takagi-Taupin equations. The white beam synchrotron back reflection topography revealed a sequence of strain modulation fringes similar to the main interference maxima in the rocking curves. They also confirm the uniformity of applied dose and lack of extended crystallographic defects which could be caused by implantation. The characteristic feature of the evaluated profiles was the existence of the deformed region close to the surface which points that the deformation is mainly caused by point defects produced by incident ions and recoils. The other feature increasing with the temperature of implantation was the flattening of top part of the strain maximum corresponding to the insulating buried layer.