Femtosecond Laser Micro Structure Of The Silicon Photoelectric Properties

Arrays of conical spikes can be formed on a silicon surface by cumulative irradiation of femtosecond laser pulses in the presence of ambient gases. The microstructure’s morphology depends not only on the species of the ambient gas, but also the flux of laser, and the pressure of the ambient gas. The absorption of micro-structured silicon has been measured in the visible and near infrared wavelength range of0.3μm-2.5μm. The result shows micro-structured silicon has strong absorption. The ambient gases, the height of spike and the annealing temperature will have strong influence on the absorption of micro-structured silicon. The infrared absorption of micro-structured silicon formed in ambient of SF6and N2are quite different. The absorption ratio of micro-structured silicon increases as the height of spikes increases. The higher the annealing temperature is, the lower the absorption ratio will be.Normal emissivity characteristics of micro-structured silicon are investigated. Experimental results show that the micro-structured silicon has a high normal spectral emissivity, close to the standard black body. As the height of spike increases, the normal spectral emissivity increase. The normal spectral emissivity also increases with increasing temperature. Emissivity of the micro-structured silicon coated with gold film shows an increasing trend. The high emissivity is related to the structure of the micro-structured silicon and the gold-silicon eutectic phase.Prototype devices are made by coating electrodes to the micro-structured silicon. Then photoelectric responsibility is measured. The result shows the responsibility increases as the height of spike increases. The responsibility between0.5V bias and without bias is different. The annealing temperature does play an important role on the responsibility. Generally, with the annealing temperature increases, the responsibility increase.These remarkable optical properties of micro-structured silicon show the potential to be used as silicon silicon-based wide band detectors, solar cells, radiation and so on.