IDEA #1MF59Q SEMICONDUCROR/OXIDE NANOCOMPOSOTE MATERIALS FOR RANDOM LASER APPLICATIONS

NANOTECHNOLOGIES · RESEARCH ON NANOCOMPOSITES SEMICONDUCROR/OXIDE NANOCOMPOSOTE MATERIALS FOR RANDOM LASER APPLICATIONS Description The design of the resonator in semiconductor lasers is crucial for achieving low threshold for the onset of laser action and a smaller volume of active material. The design of the resonator on highly scattering disordered media is a most easy and cost-effective way to produce a laser resonator. Semiconductor/oxide nanocomposites pro- duced on porous semiconductor and dielectric templates offer possibilities to design a wide range of random laser resonators. Media with controlled light scattering proper- ties are prepared by electrochemical dissolution of semi- conductor substrates, or by electrochemical oxidation of metallic foils. The morphology of the porous template is modeled either in the form of two dimensional structures with pores of controlled cross section stretching perpen- dicular to the substrate surface, or in the form of three dimensional structures containing crossing pores. The characteristic dimensions of the porous skeleton structure and the diameter of pores is varied from 20 to 500 nm (Fig. 1) in function of the required light scattering proper- ties. For the introduction of optical gain properties to highly scattering medium, porous semiconductor GaP, GaAs, InP and ZnSe as well as dielectric Al2O3 and TiO2 templates are doped with rare earth elements (Eu, Er) and transition metals (Cr, Ti). A variety of ZnO micro/nanostructures which act as laser resonators sustaining guided modes, whispering gallery modes, random lasing and a combination of them are produced by modifications of chemical vapour depo- sition (CVD) including low pressure CVD, atmospheric pressure metal-organic CVD and carbothermal evapora- tion (Fig. 2). The technology ensure high optical quality of the produced nanostructures to act as gain medium for stimulated emission in combination with high quality factor laser resonators. Innovative Aspect and Main Advantages One of the most important advantages of the technology proposed for the production of random laser media as compared to the state of the art analogues is the com- patibility with optoelectronic and photonic circuit integra- tion. Another advantage is the simplicity and cost effec- tiveness of the developed photon-assisted electrochemical methods for preparation of porous semiconductor tem- plates, technological methods for the preparation of laser active nanocomposite media, and technologies for the production of a variety of lasing ZnO nanostructures. The electrochemical methods provide possibilities to con- trol the degree of order and to produce random media with controlled morphology starting from discrete scat- terers with strong short-range disorder, up to smooth long-range inhomogeneity in weakly disordered media. The electrochemical technologies can be applied with neutral, environmentally friendly electrolytes. Another advantage of the proposed approach is the possibility to combine the traditional lithographic methods for the de- sign of semiconductor substrates with non-lithographic electrochemical methods of nanostructuring, i. e. the re- gion of the semiconductor substrate to be nanostructured can de defined by lithography, and the porosity can be introduced in the defined regions by electrochemistry. Areas of Application In comparison with the previously developed random lasers on powders and organic materials, the elaboration of ran- dom lasers on semiconductor substrates opens possibilities for electrical pumping instead of optical pumping, which is very important for optoelectronic applications. Apart from photonic and optoelectronic applications the random lasers are suitable for document encoding and ma- terial labeling, biomedical diagnostic, absorption spectros- copy and chemical identification. Fig.1. 2-D Er and Eu doped semiconductor/oxide nano- composites based on porous GaP layers. Fig.2. 3-D microstructures consisting of lasing ZnO nanorods. Stage of Development The methods of producing random laser media based on semiconductor and dielectric templates as well as semicon- ductor/oxide nanocomposites are protected by Moldova Patents No 3705, 3711, 3789, 3811, 3822. The results of characterization are published in: - Phys. Stat. sol. (RRL) 1, No. 1 (2007) R13-R15, “Er- and Eu-doped GaP-Oxide porous composites for optoelec- tronic applications”. J. Opt. A:Pure Appl. Opt. 9 (2007) 401-404 “Red and green nanocomposite phosphors prepared on porous GaAs templates”. J. Opt. A: Pure Appl. Opt. 11 (2009) 075001. “Whisper- ing gallery modes and random lasing in ZnO microstruc- tures. J. Phys. D.: App. Phys. 42 (2009) 095106. “A comparative study of guided modes and random lasing in ZnO nanorod structures”. - - - Contact Details Contact person: Veaceslav Ursachi Institute of Applied Physics, Academy of Sciences of Moldova. Address: Chisinau 2028, Academy str. 5, r. 245 Tel.: (373-22) 23-75-08; 73-86-05 fax.: (373-22) 73-81-50; E-mail: ursaki@yahoo.com Web-site: www.phys.asm.md