Comparative studies of nanoscale columnar AlxGa1-xN/AlN heterostructures grown by plasma-assisted molecular-beam epitaxy on cSi, porSi/cSi and SiC/porSi/cSi substrates

Problems of the growth of nanoscale columnar AlxGa1-xN/AlN heterostructures on hybrid substrates involving porous silicon and silicon carbide layers by molecular beam epitaxy technique with plasma-activated nitrogen are discussed in this study. The epitaxial growth of nanoscale columnar AlxGa1-xN/AlN heterostructure is shown to be specified by the layer of silicon carbide, which is formed by atomic substitution technique, and a porous silicon sublayer predetermines the oriented growth of SiC. The performed complex of structural-spectroscopic analysis demonstrated that epitaxial growth of the nuclear AlN layer on all types of the substrates in N-enriched conditions resulted in the formation of AlxGa1-xN/AlN heterostructures with Ga-polar surface. At the same time it was found that the layer of ordered AlxGa1-xN alloy was formed only on the hybrid SiC/porSi/cSi substrate. The layer of AlxGa1-xN on the substrates of cSi and porSi/cSi is present in the state of disordered alloy with an excess content of gallium atoms. Nanocolumns of AlxGa1-xN/AlN grown on the hybrid SiC/porSi/cSi substrate have two types of preferential azimuthal orientation that affects not only their structural and optical properties but also the value of elastic deformation in the heterostructure nanoscale layers. For the first time, azimuthal dependence of intensity of E1(TO) and E2high photon modes was detected in the Raman spectra. The observed periodicity angle in micro -Raman scattering coincides with the characteristic swivel of nanoscale columns of AlxGa1-xN/AlN around c-axis according to the data of XRD pole figure measurements. Results obtained in our work show promising capabilities in the use of SiC/porSi/cSi substrates for integration of silicon technology and technology of synthesis of the nanoscale columnar AlxGa1-xN heterostructures by molecular-beam epitaxy with plasma-activated nitrogen.