飞秒激光改性6H-碳化硅晶体表面光电导增益现象研究

Enhancement of surface photoconductivityin 6H-silicon carbide crystal modified by femtosecond laser pulse irradiation

半绝缘6H型碳化硅(6H-SiC)具有高电阻率性质,在可见光照射下进行光电导测量时,通常光生电流很小;然而经过飞秒激光辐照改性之后,发现在可见光波段的光电导有明显的增益.本文利用紫外-可见-近红外吸收谱、X射线光电子能谱和发光光谱测量分析了激光改性之后碳化硅样品的光谱吸收、发射和晶体元素比例变化情况.分析认为碳化硅光电导增益的原因是飞秒激光辐照过程改变了碳化硅表面的硅碳元素的原子浓度比,形成新的物质结构形式,从而导致了表面光电导性能的提高.

The photocurrent is very small when the visible light irradiates the semi-insulating silicon carbide. The femtosecond laser pulses are used to modify the silicon carbide surface, and the result shows that the photocurrent is enlarged several times according to the measurement results of photoconductivity. In order to explain the reasons for this change, some characterization means are employed, including the absorption, emission and X-ray photoelectron spectra. There are found some changes in the absorption spectra and emission spectra, and also in the silicon and carbon atom ratio according to the test results of X-ray photoelectron spectrum. We think that the changes of the crystal structure and atom ratio between silicon and carbon lead to the change of electronic energy band structure and the occurrence of many defect states. As a result, the photocurrents are improved in the range of visible light on the surface of 6H-SiC after the femtosecond laser pulses have irradiated the surface.