Nanostructured surfaces

Optical properties of cadmium chalcogenide substrates with surface nanostructure
Mazur T.M 1,2, Mazur M.P.2, Makhniy V.P.3, Berezovskiy M.M.3, Kinzerska O.V.3, Slyotov M.M3
1 Vasily Stefanik Prikarpathian National University Shevchenko, 57, Ivano-Frankivsk-76018, Ukraine.
E-mail: tetiana.mazur@nung.edu.ua 
2 Ivano-Frankivsk National Technical University of Oil and Gas Karpatska, 15, Ivano-Frankivsk-76019, Ukraine.
3 Yuriy Fedkovych Chernivtsi National University Kotsyubynsky, 2, Chernivtsi-58012, Ukraine.

Obtaining, research and practical use of semiconductor substrates with surface nanostructure (SSN) is one of the most interesting and promising areas of solid-state electronics. This paper discusses the physical causes of the transformation of the optical properties of cadmium chalcogenides caused by SSN. The latter were created by annealing in air under certain conditions of single-crystal CdTe, CdSe and CdS substrates with electronic conductivity. Analysis of the AFM topograms of the surfaces of the annealed samples shows that it consists of small pyramidal elements with lateral dimensions of 10-50 nm, which can be combined into larger ones with dimensions of 100-300 nm. The most characteristic feature of substrates with SSN is the appearance of the B band in the luminescence spectra in the photon energy range, which is significantly larger than the band gap Eg of the base material. Its presence is explained by the size quantization of the energy of charge carriers in small nanopyramids, and the anomalously large half-width of the B-band is due to the dispersion of their sizes. Another feature of samples with SSN is a significant increase in the efficiency of the η edge radiation (A-band), which is not observed at all at 300 K in CdTe base substrates. The effect of increasing η is associated with a decrease in the surface recombination rate caused by the formation of SSN. Larger nanopyramids (100-300 nm) take part in scattering and multiple reflection of radiation, which leads to a decrease in the absolute value of optical transmission, as well as a shift of its spectral edge to lower energies compared to Eg of the base material. The issues of optimizing the annealing modes to achieve maximum efficiency of the edge luminescence of the materials used are discussed.