LIGHT EMITTING “POLYMER-NANOPARTICLES” COATINGS ON MACROPOROUS SILICON SUBSTRATES

We investigate the conditions for increase of the photoluminescence of CdS nanocrystals in polyethyleneimine and polyethyleneimine with carbon multiwall nanotubes on macroporous silicon substrates. Macroporous silicon structures are made using the photoelectrochemical etching of n‑Si wafers. Macropores with diameter D p  = 2¸5 mm, depth h p  = 40¸120 mm and concentration N p  = (1¸6)×10 6  cm ‑2  were formed. CdS nanocrystals of 1.8–2 nm in size are synthesized in reaction between Cd 2+  and HS -  in a colloidal solution of polyethyleneimine in water.  C arbon multiwall high purity nanotubes with submicron length and 20 nm diameter were produced by catalytic pyrolysis of unsaturated hydrocarbons. “Polymer-nanoparticles” coatings are deposited from a colloidal solution in water on single crystalline silicon, macroporous silicon and oxidized macroporous silicon. The maximal  photoluminescence intensity  of  CdS  nanocrystals is  measured  f or the  oxidized  macroporous silicon  substrates  with maximal electric field strength  at  the Si- SiO 2  interface . The photoluminescence quantum yield of CdS  nanocrystals  on the surface of oxidized macroporous silicon increases with  time and reaches 28 %. Photoluminescence of polyethyleneimine with carbon multiwall nanotubes on macroporous silicon with microporous layer is 3–6 times more intense as compared with substrates c-Si, macroporous Si and oxidized macroporous Si due to a non-radiative proton recombination decrease at the silicon matrix boundary with microporous layer and nanocoating.