Photoreflectance study of multilayer structures of nanocrystalline CdSe in insulator matrix

Nanocrystalline multilayer structures of CdSe/SiOx and CdSe/GeS2, with layer thickness varying from 2.5 to 10 nm, were grown by a modified conventional vacuum thermal evaporation technique [R. Ionov and D. Nesheva, Thin Solid Films 213(2), 230 (1992).]. Low temperature photoreflectance (PR) measurements at 20 K reveal dependence of the energy band gap on the layer thickness. This dependence is for the CdSe/SiOx multilayer structures in good agreement with previously published theoretical predictions [D. Nesheva, C. Raptis, and Z. Levi, Phys. Rev. B 58(12), 7913 (1998).] of hole confinement in a potential well of Uh ≈ 1.3 eV in the CdSe sublayers. For the CdSe/GeS2 multilayers, it is the first direct experimental evidence of the low dimensionality of these structures. Based on the experimental results obtained, a schematic band diagram of these multilayers is suggested. Due to the low cost of the growth techniques, the nanocrystalline multiquantum wells studied may prove of high technological interest for optoelectronic applications.