Liu Caichi

Improving light trapping and conversion efficiency of amorphous silicon solar cell by modified and randomly distributed ZnO nanorods

Three-dimensional (3D) nanostructures in thin film solar cells have attracted significant attention due to their applications in enhancing light trapping. Enhanced light trapping can result in more effective absorption in solar cells, thus leading to higher short-circuit current density and conversion efficiency. We develop randomly distributed and modified ZnO nanorods, which are designed and fabricated by the following processes: the deposition of a ZnO seed layer on substrate with sputtering, the wet chemical etching of the seed layer to form isolated islands for nanorod growth, the chemical bath deposition of the ZnO nanorods, and the sputtering deposition of a thin Al-doped ZnO (ZnO:Al) layer to improve the ZnO/Si interface. Solar cells employing the modified ZnO nanorod substrate show a considerable increase in solar energy conversion efficiency.

Gettering of metal impurities in silicon by fast neutron irradiation

Some irradiated defects were introduced into p-type CZ Si by fast-neutron irradiation, they interact with oxygen in CZ Si during high temperature annealing, enhance the oxygen out-diffusion on the wafer surface and promote the precipitation of oxygen in the silicon bulk. Utilizing the combination of fast-neutron irradiation and intrinsic gettering (IG), a new excellent gettering technology only with one-step high temperature heat-treatment was invented, instead of multistep processing in conventional IG technology. With our new gettering technology, the metal impurities (Fe,Ni) on the surface of p-type <111>-oriented CZSi wafers was efficiently inhibited.

Electrical and Optical Characterization of n-GaN by High Energy Electron Irradiation

The effect of high energy electron irradiation on the electrical and optical properties of n-GaN is studied. Hall and photoluminescence measurements are carried out on the samples irradiated with different doses. The results obtained from Hall measurements show that electron concentration and mobility are proportional to electron irradiation doses. The PL results show that the near-band-edge intensity and yellow luminescence intensity decrease continually with the increasing electron irradiation. However, it is found that the ratio of the yellow luminescence intensity to the near-band-edge intensity increases with the increasing of electron irradiation dose. To interpret this phenomenon, we propose two theoretical models based on the charge transport mechanism and rate equations, respectively, and they are in good agreement with the experimental observations.

Room-Temperature Ferromagnetism in Zn1−xMnxO Thin Films Deposited by Pulsed Laser Deposition

Zn1−xMnxO (x = 0.01–0.1) thin films with a Curie temperature above 300 K are deposited on Al2O3 (0001) substrates by pulsed laser deposition. X-ray diffraction (XRD), ultraviolet (UV)-visible transmission and Raman spectroscopy are employed to characterize the microstructural properties of these films. Room temperature ferromagnetism is observed by superconducting quantum interference device (SQUID). The results indicate that Mn doping introduces the incorporation of Mn2+ ions into the ZnO host matrix and the insertion of Mn2+ ions increases the lattice defects, which is correlated with the ferromagnetism of the obtained films. The doping concentration is also proven to be a crucial factor for obtaining highly ferromagnetic Zn1−xMnxO films.

Epitaxial lateral overgrowth of gallium nitride without mask on sapphire

GaN has attracted great interest world wide during these years. Epitaxial growth technique such as epitaxial lateral overgrowth (ELO) has been proved to be a very effective way to produce a high-quality GaN layer, so many studies made researches on this field. In this work, GaN was deposited on sapphire c side (0001) wafers as the ELO theory without mask by metal organic chemical vapor deposition (MOCVD). The growth mechanism was also analyzed and the properties of GaN layer were investigated by double-crystal X-ray diffraction, atomic force microscopy and wet chemical etching. The result proved that higher-quality GaN layer was received using this method