Электрические и оптические характеристики пленок из наночастиц Si, нанесенных на подложки высоковольтным электронапылением из золей в этаноле

The paper describes the results of studying the opticaland electrical characteristics of films made of silicon nanoparticles(nc-Si) deposited on substrates by high-voltage electrospray fromsols of nc-Si in ethanol. It was found that the interaction of ethanoldroplets carrying nc-Si with an electric field of corona dischargeleads to polymerization of ethanol and formation of a polymerlayer on the nanoparticle surface. The geometry and electric fieldstrength in the flow area of ethanol droplets could be changedby means of the focusing electrode in the high-voltage device.As a result we could make nc-Si films with different kind ofpolymer layer on Si nanoparicle surface: nc-Si A and nc-Si B (thefilms deposited without and with focusing electrode, respectively).The optical band gap Eg of nc-Si A films increased from 1.9to 2.2 eV after annealing at the temperatures from room oneto 400◦C in air atmosphere. The Eg of the nc-Si B films wasindependent on annealing and was 1.85 eV. The constancy of Egin nc-Si B films is explained by the polymer properties on the Sinanoparticles surface in these films and more effective blockingthe penetration of oxygen atoms from the surrounding atmosphereduring annealing to temperatures of 400◦C than in the case of thepolymer in nc-Si A films. The temperature dependences of theconductivity (dark and photo) of nc-Si A films are approximatedwith good accuracy by two exponential functions, the darkactivation energies of the films being approximately equal to 0.75and 0.1 eV. The conductivity of nc-Si A films decreased noticeablywhen illuminated with radiation in the range 460−470 nm Thetemperature dependences of the conductivity of nc-Si B films withgood accuracy is approximated by one-exponential function of theactivation type with activation energies of 0.73 (dark) and 0.59 eV(photo). In contrast to the nc-Si A films, the photoconductivityof nc-Si B films increase by more than 4 times with respect tothe dark conductivity when the films were illuminated anologically.The nc-Si B films are photoactive, since sandwich-like structures ofAl/nc-Si B/Al can generate emf. The dark and photo-conductivityof nc-Si A films in the voltage range > 2V is determined by thetwo-center Poole−Frenkel effect, the concentration of the centersthat determine the character of the Poole−Frenkel conductivitywas 3 · 1017 cm−3. In nc-Si B films in the voltage range 2−5V, theelectronic transport is determined by space-charge-limited currents(SCLC) and at higher voltages by the two-center Pool−Frenkelconduction. The concentration of traps contributing to SCLC in thefilms is 4 · 1016 cm−3. The concentration of the Pool−Frenkelcenters, decreases from 3 · 1016 to 2 · 1014 cm−3 with decreasingtemperature in the range 120−400◦C according to the activationlaw with an activation energy of 0.7 eV.