In this work, we present the enhancement of ultraviolet (UV) photodetection of Ag-ZnO thin film deposited by radio frequency magnetron sputtering. The surface morphological, optical, structural, and electrical properties of the deposited thin films were investigated by various characterization techniques. With this Ag-ZnO thin film structure and proper geometry of metal–semiconductor–metal (MSM) interdigitated structure design, photocurrent enhancement has been accomplished. MSM-photodetectors (PDs) using structures of Ag-ZnO gave a 30 times higher magnitude photocurrent at 340 nm of the wavelength. Plasmon-induced hot electrons contributed to improved spectral response to the UV region, while absorption and scattering effect enhanced broadband improvement to a response in the VIS–IR spectrum range. The improvement of Ag-ZnO PD in comparison with ZnO is attributed to the surface plasmon effect using Ag nanodisks. These results indicate that Ag-ZnO thin films can serve as excellent ultraviolet-PD and a very promising candidate for practical applications.
Plasmon field-effect transistor is a hybrid device using nanostructures to detect the plasmonic energy. This device efficiently transfers plasmonic hot electrons from the metal nanostructures to the semiconductor. The transported hot electrons to the electron channel increases transistor drain current. We investigate the efficiency of plasmonic hot carrier harvesting between metal and semiconductor. We analyzed the effect of gold nanoparticle (NP) density and distribution on plasmon FET spectral response. Then, we studied electric field-assisted hot electron transfer and transport using different device structures. The position of plasmonic structures plays an important role in plasmonic energy detection efficiency because the gradient of electric field seen by induced hot electrons varies depending on the distance between drain and source. Both the experimental and simulation results confirm that by fabricating the gold NPs close to source the spectral response increases by 31% in comparison with having gold NPs close to the drain. Our simulation and experimental data suggest important design considerations to improve hot electron collection and conversion using metallic nanostructures for plasmonic energy harvesting.
In our study, the polycrystalline Si thin films were grown for solar cell applications by using the metal-induced growth (MIG) process. In this process, the poly-Si heteroepitaxally grows from the NiSi2 or CoSi2 layers which were formed by the reaction of Ni or Co with Si. Usually, due to the low absorption of light in the crystalline Si, light confinement is an important issue in thin film poly-Si solar cells. The MIG poly-Si thin films have some intrinsic features which assist the light absorption and light trapping. First, the top surfaces of the poly-Si films are relatively rough and have grain facets which reduce the light reflectance. In comparison, the Ni-induced Si film has hemisphere-shaped grain tops while Co-induced Si films have pyramid-shaped grain tops. The Ni-induced Si film has a rougher top-surface, so it appears to be darker under the optical examination compared to the Co-induced sample. This implies that more light may be absorbed in the Ni-induced Si film than in the Co-induced one. Second, in the MIG process, a thin metallic layer under the Si film was formed as a seed-layer for Si growth. This metallic layer could serve as a back contact and a back surface reflector. The above top and back surface structures are naturally formed and will allow MIG poly-Si to absorb the light more efficiently than other techniques. So far, the Schottky solar cell which was fabricated for the intent of MIG poly-Si film property studies has shown a Jsc of 12 mA/cm2. By considering the Si film thickness of 5 μm and the photon absorption of 60% at this thickness, these data are reasonable.