Influence of the substrate in the (Ga,Al) alloy interface microstructure studied by X-ray diffraction

Full text: In this work, X-ray diffraction techniques are used to investigate the effect of the substrate in the (Ga,Al) alloy interface microstructure. These alloys are deposited as balloons by Low Pressure - Metalorganic Chemical Vapor Deposition (LP-MOCVD) onto different substrates: Si(001), GaAs(001) and Al2O3(1102) and then, submitted to NH3 flow at different temperatures between 650 and 750 deg C in order to favor the growth of Ga and Al nitrides on the substrates. X-ray diffraction techniques such as: grazing incidence, reflectivity measurements and multiple diffraction have been used to characterize these samples. The measurements were performed in a Philips X-PERT PRO MRD system with a thin lm geometry and also in a multiple diffraction laboratory set up. Preliminary results using grazing incidence allowed to confirm the presence of GaN in these structures independently on the chosen substrate. The first reflectivity measurements have provided the characteristic fringe pattern associated to grown structure/substrate system. The simulation of this pattern allows to obtain structural information (density, thickness and roughness) on the deposited structure. The analysis of the multiple diffraction pattern, i.e., the Renninger scan ( φ-scan) using the (002) primary reflection, give information on the distortion of the substrate unit cell parameters caused by the structure deposition process by measuring the (35 - 1)(353) four-beam sensitive case. Furthermore, information on the substrate surface can be obtained from the detailed investigation of the Bragg Surface Diffraction (Bs), in this case, all (h,k,l=1) strong secondary peaks. (author)