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The optical properties of sub-100 nm raspberry-like nano-systems composed of highly monodisperse silica particles and large gold nanoparticles (GNPs) is studied experimentally. The nanoparticles (NPs) were prepared by a self-assembly method, and the pH of each solution was determined by measuring the ζ-potential to ensure the stability of the nano-systems. Dynamic light scattering measurements show a narrow size distribution of NPs, and fairly dispersed particles in solution. The obtained nanoraspberries was also studied by transmission electron microscopy, which shows that the GNPs closely packed on the surface of silica particles. This effect induced a broadening and a shift of the absorption band to higher wavelengths, with an increase in GNPs density. It was also observed that the reduced size of silica particles resulted in a shortening of the inter-particles distance, which has favoured the generation of many hot spots in the gaps between GNPs. The tenability of obtained plasmon bands may have benefits in SERS probe, photocatalysis and fluorescence-based bioimaging.

A two-dimensional model of a metal-semiconductor-metal (MSM) ZnO-based photodetector (PD) is developed. The PD is based on a drift diffusion model of a semiconductor that allows the calculation of potential distribution inside the structure, the transversal and longitudinal distributions of the electric field, and the distribution of carrier concentration. The ohmicity of the contact has been confirmed. The dark current of MSM PD based ZnO for different structural dimensions are likewise calculated. The calculations are comparable with the experimental results. Therefore, the influence with respect to parameters s (finger spacing) and w (finger width) is studied, which results in the optimization of these parameters. The best optimization found to concur with the experimental results is s = 16 µm, w = 16 µm, l = 250 µm, L = 350 µm, where l is the finger length and L is the length of the structure. This optimization provides a simulated dark current equal to 24.5 nA at the polarization of 3 V.OCIS codes: 040.5160, 250.0250, 160.6000. doi: 10.3788/COL201109.100401.Extremely complex, integrated photonic circuits are developed and industrially produced. This is in consideration of the demand for low-cost high-bandwidth circuits, and the demand for knowledge control regarding the manufacturing processes of semiconductor optoelectronic components. The metal-semiconductor-metal (MSM) photodetector (PD) is a good choice in the photo detection field due to the simplicity of manufacture and suitability for monolithic integration [1,2] . Indeed, the planar structure of MSM PD results in an exceptionally small capacity, which is highly desired for highbandwidth and low-noise performance [3] . Recently, general manufacture of MSM PD used semiconductor materials with wide and direct gaps. The ZnO with direct gap (3.3 eV) has attracted considerable interest because of its excellent electrical properties that allow wide application in high temperatures and high pressures, as well as in the fabrication of components needed to address very high response time [4,5] . Furthermore, ZnO has high sensitivity in ultra-violet detection, making it one of the detectors popularly used for monitoring air quality and gas detection, as well as in military applications [6−8] . In recent years, a significant number of studies have focused on the MSM PD based ZnO, using different metals for interdigitated contacts. Majority of these studies were experimental [9−11] , with only a few focusing on the theoretical aspect. The model construction is important in understanding a certain number of physical phenomena that may be difficult to achieve experimentally because of the high cost and time requirement, particularly those of advanced technologies. Controlling transport phenomena in MSM PDs by modelling with numerical methods is especially important in the present case because specific materials such as undoped ZnO are used. Other researchers have developed the subject using simulators, such as COSMOL multiphysics [12,13] . In the present work, a...

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