Nanooptics and photonics
Photonic modes in 2D macroporous silicon structures with nc-CdTe and SiO2 nanocoatings
L. Karachevtseva, O. Lytvynenko, K. Konin, O. Stronska

Department of Photonic Semiconductor Structures, V. Lashkaryov Institute of Semiconductor Physics, NASU, Prsp. Nauki, 41, Kiev-03028, Ukraine. 
E-mail: lakar@isp.kiev.ua

The near-IR light absorption in the periodical 2D macroporous silicon structures with coatings of CdTe nanocrystals [1] and SiO2 layers [2] were investigated. The amplitude of oscillations is maximal in the spectral range of surface level absorption. This process is a result of the resonance electron scattering on impurity states. The macroporous silicon structures with coatings have high potential of heterojunction between the silicon matrix and nanocoating. Therefore, the onset of giant oscillations can be attributed to the electro-optical processes in strong electric field. The electric field intensity in the surface heterojunction area Fs is determined by the oscillation period in the macroporous silicon structures and is equal to 104-105 V/cm.                                    
The peculiarities in absorption spectra of macroporous silicon structures with CdTe nanocrystal layer of 200 nm thick and SiO2 layer of 800 nm thick are similar to those observed in reflectance spectra of macroporous silicon photonic crystals at near-normal light incidence. The critical points in absorbance are related to photonic modes excitation as an “absorption” process that includes intensity of diffracted beams.
The oscillation period and electric field strength in the macroporous silicon structures with thick SiO2 nanocoatings fluctuate about a constant value at low photon energies and become quadratic in photon energy, depending on the geometrical sizes of silicon matrix and SiO2 nanocoatings. The relevant electric field strength growth corresponds to the quasi-guided mode formation in the silicon matrix (minimal distance between the macropores) and in the silicon column.
Photonic modes do not coincide with quasi-guided modes in the silicon matrix as well as do not appear in absorption spectra of  macroporous silicon structures with coatings at arbitrary macropore distribution.
1.	Karachevtseva L., Goltviansky Yu., Sapelnikova O., Lytvynenko O., Stronska O., Bo Wang, Kartel M. Wannier–Stark electro-optical effect, quasi-guided and photonic modes in 2D macroporous silicon structures with SiO2 coatings // Appl. Sur. Sci.–2016. – 388, №1.– P. 120–125.