Peihong Cheng

Enhancement of ZnO light emission via coupling with localized surface plasmon of Ag island film

Enhancement of the light emission of ZnO films was observed by coupling through localized surface plasmons. By sputtering Ag islands onto ZnO films, their band gap emission coming through the Ag island films was enhanced by threefolds, while the defect emission was quenched. The enhancement was found to be mainly dependent on the sputtering time of the Ag islands, which is related to the island size. Furthermore, the relative spectral position between the ZnO emission band and the localized surface plasmon resonance bands of Ag islands was found to be decisive for the enhancement or quenching of photoluminescence, indicating that the emission intensity of ZnO films can be controlled by the Ag island size and the localized surface plasmon resonance band position.

Electroluminescence of SnO2∕p-Si heterojunction

Polycrystalline SnO2 film of tetragonal rutile structure with an optical band gap of 3.9eV was formed by oxidation process at 1000°C on electron beam evaporation deposited Sn film. Room temperature electroluminescence from the SnO2∕p-Si heterojunction was observed at 590nm when the device was under sufficient forward bias with the positive voltage applied on the p-Si substrate. It is proposed that the electrons in the conduction band of SnO2 relax to defect states that resulted from the dangling bonds at the surface of the small SnO2 grains and then radiatively recombine with the holes in the valence band.

Localized surface plasmon enhanced photoluminescence from ZnO films: Extraction direction and emitting layer thickness

The light emission from ZnO films is enhanced by localized surface plasmon (LSP) of Ag island films. The dependence of LSP coupled emission on light-extracting direction and the thickness of ZnO films is investigated. It is found that the photoluminescence (PL) enhancement factors for upward extraction are much smaller than those for downward extraction. This is ascribed to the low transmittance and nonradiative absorption loss of Ag films. The near-field effect of LSP results in the dependence of the PL enhancement of ZnO films on the film thickness. A maximum PL enhancement factor of more than 15 is obtained when the thickness of ZnO was about 40 nm.

Influence of substrates in ZnO devices on the surface plasmon enhanced light emission

The substrates in emitting structure were found to have an influence on the surface plasmon mediated light emission of ZnO films. Ag film mediated photoluminescence was quenched for ZnO on silicon substrate but enhanced for ZnO on quartz or sapphire substrate. Through a theoretical simulation, the quenching for ZnO on silicon substrate is ascribed to the power lost to the substrate mode nonradiatively at the expense of the power coupled to the SP mode. The substrate with a high refractive index may capture and dissipate the emitting power which limits the efficiency of SP mediated light extraction. Therefore, a proper arrangement of the refractive index of the substrate and emitting layers in the device structure is decisive for the SP coupled light emission enhancement. Base on the theoretical analysis, a four-layered structure was advanced to recover SP mediated emission enhancement from ZnO film on silicon substrate.

Enhanced red electroluminescence from a polycrystalline diamond film/Si heterojunction structure

Strongly enhanced red electroluminescence (EL) was realized at room temperature (RT) from a polycrystalline diamond film (PDF)∕n−-Si heterojunction fabricated by direct chemical vapor deposition of PDF on silicon substrate. The red EL peaks featuring fairly narrow linewidth (∼12nm) were obtained when the device was under sufficient reverse bias with the positive voltage applied on the silicon substrate. Cathodoluminescence spectra measured from 77K to RT suggested that the enhanced red EL peaks originated from the neutral vacancy induced intrinsic defects of the PDF rather than the Si-related centers. The carrier transport mechanism of the PDF∕n−-Si heterojunction was elucidated based on the proposed energy band diagram of the PDF∕n−-Si heterojunction.

Light absorption enhancement of amorphous silicon film coupled with metal nanoshells

Increasing the light absorption in the weakly absorbing near-bandgap region is of great significance for improving efficiency in a thin-film silicon solar cell. In this study, light absorption enhancement near the infrared domain was realized by coating Ag nanoshells on the front side of amorphous silicon film. Detailed investigations prove that the enhancement can be related to the excitation of localized surface plasmons (LSPs). LSP scattering-induced light coupling in the guided mode, intense in-phase interference between the scattering field and the transmitted field, and the Floquet mode were observed in the simulated E-field profile, and the significant absorption enhancement was accounted for by these effects.

Metal semishell-substrate coupled structures with enlargened near-field enhancement area

Metal antennas-substrate coupled structures have unique features of strong nanoscale light confinement and field enhancement at the gap, which make them attractive and promising in a variety of applications such as sensing, lasing, and solar cell. Here, we built a coupled system consisting of a gold spherical semishell antenna and gold substrate. Through numerical simulation, it is found that due to the unique geometric shape of the antenna, the near-field enhancement area of the localized resonance is enlarged dramatically in the designed plasmonic structure, which is beneficial to increasing the active region, allowing more molecular adsorbed and also replaced easily. Moreover, the far-field extinction spectra of the localized dipole mode in the designed structure has higher quality factor and is more robust to the gap separation than its solid counterpart, which may relax the fabrication tolerances.

Role of dielectric film in metal grating for improved polarized transmittance in 0.9–1.7 µm range

It is found that the TM light transmittance and polarized extinction ratio in the near infrared range (0.9–1.7 µm) can be greatly increased by incorporating a dielectric layer between metal gratings (MGs) and high refractive index substrate (InP). The role of the dielectric layer and the physical mechanism of the polarized transmittance improvement are elucidated based on numerical simulation. Besides anti-reflection role as it is known to all, the incorporated dielectric layer is found eliminating energy losses from the Rayleigh anomalies and surface plasmon (SP)-cavity mode between adjacent metal grids. By optimizing the refractive index and thickness of the dielectric layer, it is demonstrated that the TM transmittance at the central wavelength (1.3 µm) can reach above 95% for Au MG with the period as large as 400 nm.

Photoluminescence enhancement of Silicon-rich silicon nitride film induced by silver localized surface plasmon

The photoluminescence of silicon-rich silicon nitride (SRSN) film was enhanced by coupling with the localized surface plasmon of Ag island film. It is found that the deposited Ag film induces an enhancement of excitation of SRSN film through increasing the absorption of SRSN film. Furthermore, it is demonstrated that the emission enhancement is much more decided by the excitation wavelength than by the Ag island scattering.