E. E. Yakimov

Photoelectric properties of ZnO films doped with Cu and Ag acceptor impurities

The influence exerted by doping with Cu and Ag acceptor impurities at a content of 1, 3, and 5 at. % on the luminescence and photoconductivity of zinc oxide films has been studied. Electron-beam evaporation in optimal modes has been used to obtain films with predominant luminescence in the UV spectral range. It has been shown that the incorporation of copper yields three types of point defects in ZnO: CuZn (3d10), CuZn (3d9), and Cui; and in silver, a single type: AgZn (3d10). Precipitation of a silver oxide phase at the highest impurity concentration has been observed. Impurity incorporation leads to a pronounced increase in the resistance and photosensitivity of films.

Vapor phase synthesis of aligned ZnO nanorod arrays from elements

A vapor phase process is described for the synthesis of one-dimensional zinc oxide nanocrystal arrays. Using this process, well-aligned ZnO nanorod arrays are grown on (100) Si substrates with no catalyst. Cathodoluminescence, x-ray diffraction, and electron microscopy results demonstrate that the nanorods are characterized by high purity, stoichiometric composition, and perfect crystal structure.

Elemental vapor-phase synthesis of nanostructured zinc oxide

We systematize experimental data on the elemental vapor-phase synthesis of zinc oxide nanocrystal arrays on substrates. This process may yield nanostructures differing in shape and dimensions, in particular, well-aligned ZnO nanorod arrays. A model is proposed in which aligned zinc oxide nanorod arrays may grow by the vapor-liquid-solid (VLS) mechanism, and liquid zinc nanodroplets forming on the substrate surface at the beginning of the process catalyze one-dimensional growth. The VLS process is accompanied by zinc oxide deposition onto the lateral surface of the nanorods from the vapor phase. The relative rates of these processes influence the shape of the nanorods and the thickness of the polycrystalline underlayer. Optimizing the deposition conditions, one can grow uniform arrays of aligned high-quality ZnO nanorods with no catalysts and with no special substrate preparation steps.

Luminescence of CdSe/ZnS quantum dots infiltrated into an opal matrix

The effect of the photonic band gap in the photonic crystal, the synthesized SiO2 opal with embedded CdSe/ZnS quantum dots, on its luminescence in the visible spectral region is studied. It is shown that the position of the photonic band gap in the luminescence and reflectance spectra for the infiltrated opal depends on the diameter of the constituent nanospheres and on the angle of recording the signal. The optimal conditions for embedding the CdSe/ZnS quantum dots from the solution into the opal matrix are determined. It is found that, for the opal-CdSe/ZnS nanocomposites, the emission intensity decreases and the luminescence decay time increases in the spatial directions, in which the spectral positions of the photonic band gap and the luminescence peak of the quantum dots coincide.

Effect of Nanosphere Size on the Luminescence of Synthetic Opal

We have studied the effect of the stop band and coupled photonic modes on the visible luminescence of synthetic opal photonic crystals. The results demonstrate that the position of the photonic stop band in the luminescence spectrum of opal depends on the nanosphere diameter. Optical measurements have been used to determine the refractive index of the photonic crystals and the silica sphere diameter. We have assessed the effect of coupled modes in opal on its intrinsic luminescence spectrum. Coupled modes of visible light in opal can be visualized by applying a matte sapphire plate to the opal surface.

Effect of chemical etching on the luminescent properties of zinc oxide nanorods

Vertically aligned ZnO nanorods grown on (100) Si substrates have been found to have a polycrystalline zinc oxide underlayer. After etching in a hydrochloric acid solution, the nanorods had smaller dimensions and pointed ends. As shown by exciton spectroscopy, the nanorods had a higher structural perfection and better luminescent properties in comparison with the underlayer. The 4.2-K luminescence spectra of the nanorods exhibit violet emission due to bound and interacting excitons. The low-temperature edge emission of the ZnO underlayer is shown to consist of lines due to electron-hole plasma recombination.

Luminescence from ZnO quantum dots deposited with synthetic opal

Photoluminescence from ZnO layers of varied thickness deposited onto the surface of synthetic opal has been studied. Narrow peaks of luminescence in the excitonic spectral range, related to quantum confinement of the electron wave functions, have been observed. The formation of ZnO quantum dots (QD) within the opal voids in the second subsurface layer has been confirmed by atomic force microscopy and by studying the angular dependence of the luminescence spectra.

Mode structure of laser emission from ZnO Nanorods with one metal mirror

The effect of the length of ZnO nanorods (500 nm in diameter) on the mode structure of their lasing in the ultraviolet spectral region is studied by optical luminescence microscopy. It is shown that separate nanorods with a metal mirror at one of the end faces exhibit only two or three laser modes at small nanoresonator lengths (8–20 μm). The different optical losses of longitudinal and transverse waveguide modes are established for nanorods lying on a glass substrate. An increase in the optical Q factor and a decrease in the lasing thresholds can be attributed to optical reflection from the metal mirror at the end face of the nanorod.

Ultraviolet Luminescence of ZnO Infiltrated into an Opal Matrix

Technology for the infiltration of zinc oxide into a three-dimensional opal lattice using chemical deposition from a solution was developed. Samples of ZnO-opal composites, whose luminescence at room temperature mainly occurs in the ultraviolet spectral range, were obtained. The filling ratio was monitored by two different techniques: (i) checking the increase in the mass of the sample and (ii) checking the shift of the peak in the optical reflection spectrum of samples filled with ZnO in comparison with the initial opal matrices. The results obtained by these two methods are consistent with each other. Optimum conditions for synthesizing ZnO-filled opals in order to attain the highest intensity of ultraviolet luminescence were determined. It was shown that using “raw” opals, whose voids are incompletely filled with the semiconductor material, leads to a severalfold increase in the intensity of the edge excitonic emission band at room temperature. The results obtained can be used in the development of efficient directed laser light sources in the ultraviolet spectral range based on the “photonic crystal” effect.

Aligned arrays of zinc oxide nanorods on silicon substrates

Experimental data on the elemental vapor-phase synthesis of aligned arrays of ZnO nanorods on Si substrates are summarized. A model of the self-catalytic growth of ZnO nanorods via the vapor-liquid-crystal mechanism, in which liquid Zn droplets serve as a catalyst for oriented growth, is presented. The method developed in the study provides a means for the deposition of aligned arrays of ZnO nanorods onto differently oriented Si substrates without the preliminary deposition of a metal catalyst film or a thin layer of ZnO nuclei. The influence of various factors on the growth rate, dimensions, shape, and ordering of ZnO nanorods is considered. The ZnO nanorods produced in the study are high-purity single crystals with a low content of point defects and, thus, are suitable for practical use in optoelectronics as well as in sensor and microsystem technologies.