GaP layers grown on GaN with and without buffer layers

The growth of GaP layer on GaN with and without buffer layers by metal-organic chemical vapour deposition （MOCVD） has been studied. Results indicate that the GaP low temperature buffer layer can provide a high density of nucleation sites for high temperature （HT） GaP growth. These sites can promote the two-dimensional （2D） growth of HT GaP and reduce the surface roughness. A GaP single crystal layer grown at 680 ℃ is obtained using a 40-nm thick GaP buffer layer. The full-width at half-maximum （FWHM） of the （111） plane of GaP layer, measured by DCXRD, is 560 arcsec. The GaP layer grown on GaN without low temperature GaP buffer layer shows a rougher surface. However, the FWHM of the （111） plane is 408 arcsec, which is the indication of better crystal quality for the GaP layer grown on GaN without a low temperature buffer layer. Because it provides less nucleation sites grown at high growth temperature, the three-dimensional （3D） growth is prolonged. The crystalline quality of GaP is lightly improved when the surface of GaN substrate is pretreated by PH3, while it turned to be polycrystalline when the substrate is pretreated by TEGa.

Fabrication of ZnO nanowall-network ultraviolet photodetector on Si substrates

ZnO nanowall networks were prepared by plasma-assisted molecular beam epitaxy without a catalyst on Si（111） substrates.The nanostructures have preferred orientation along the c axis.The nanostructures are about 10 to 20 nm thick and about 50 nm tall.The planar geometry photoconductive type metal-semiconductor-metal photodetector based on the ZnO nanowall networks exhibits a high and wide response spectrum,and no decrease from 250 to 360 nm.With the applied bias below 5 V,the dark current was below 6μA,and the peak responsivity of 15 A/W was achieved at 360 nm.The UV（360 nm） to visible（450 nm） rejection ratio of around two orders could be extracted from the spectra response.

Surface plasmon interference pattern on the surface of a silver-clad planar waveguide as a sub-micron lithography tool

A new sub-micron photolithography tool has been realized by utilizing the interference of surface plasmon waves(SPWs) on the near surface of a silver(Ag)-clad ultraviolet(UV) planar waveguide.A laser beam with a wavelength of 325 nm was incident into the waveguide core,and suffered a series of total internal reflections on the interfaces between the waveguide core and the cladding layers.The incident light and the reflected light induced two beams of SPWs traveling in contrary directions,which interfered with each other and formed a standing wave as a sub-micron photolithography tool.A near-field scanning optical microscope(NSOM) was employed to measure the intensity distribution of the stationary wave field of the near surface of the Ag layer of the waveguide,anastomosed with theoretical values acquired by use of finite difference time domain(FDTD) simulations.And with this sub-micron photolithography tool a SMG with a period of 79.3 nm,in good agreement with the theoretical value of 80.1 nm,was inscribed on the surface of a self-processing hybrid SiO2/ZrO2 solgel film for the first time.

Novel sol-gel material for fabrication of a long period waveguide grating filter as a precise thermometer

A new kind of organic-inorganic hybrid HfO2/SiO2 sol-gel material with a large thermo-optic coefficient and a wide linear tunable temperature range has been developed for fabrication of a long period waveguide grating （LPWG） filter, whose parameters were optimized and designed by using finite difference time domain （FDTD） simulations. The LPWG filter, a periodic rectangle-corrugated grating structure, was easily fabricated with soft-lithography technique. At a temperature range from 19~C to 70~C, the fabricated LPWG filter element demonstrated a high temperature sensitivity of about 6.5 nm/~C and a wide linear tunable temperature range of 51℃, so that it can be used as a precise thermometer. Our results are useful for the designs of LPWG filters for the implementation of a wide range of thermo-optic functions.

Enhancement of light output powers of GaN-based light emitting diodes with textured indium tin oxide transparent layer by using corrosive liquid

In order to promote the light output powers of GaN-based light emitting diodes (LEDs), two kinds of novel corrosive liquidshave been developed in this paper to roughen the surface of the indium tin oxide (ITO) current spreading layer of LEDs. As aresult, the textured transparent ITO layer greatly enhanced the external quantum efficiency of the LEDs. Provided that a wafersample was dipped in a kind of corrosive liquid developed by us for only about 60 s, the light output powers of the LEDs canbe promoted by 24.7%, compared with conventional GaN-based LEDs. It is obvious that the presented method is simple, rapidand cost-effective.