SURFACE PROCCESSING OF SEMICONDUCTOR BY THE USE OF PHOTOELECTROCHEMICAL TECHNIQUE

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Photoelectrochemical etching is a useful technique for fabricating microstructures of semiconductor surface. It affects directly the photoelectrochemical active sites and leads to a unique morphologies of the semiconductor surface depending upon certain features of the grain structures such as crystallographic orientations and presence of grain boundaries, etc.. We studied the photoelectrochemical etching site selectivity of CdSe, SrTiO_3 varistor and ZnO gas sensor.It was observed that the grain boundaries are left undissolved and both sides of the grain boundaries are deeply etched after the photoelectrochemical etching of CdSe polycrystalline electrodes under weak anodic polarization. On the contrary, the grain boundaries selectively dissolved under strong anodic polarization. We explained this etching site selectivity by energy band model of semiconductor/electrolyte interface and grain boundary potential barrier. The grain boundary potential barrier plays an important role in the semiconducting electroceramic devices such as varistors, sensors, photoeletrochemical devices etc.. The photoelectrochemical etching makes it possible to obseve visually the grain boundary potential barrier structures and affects it. We applied this etching technique to SrTiO_3 varistor and ZnO gas sensor. In the case of SrTiO_3 varistor, the onset voltage and the slope of the current varied with etching potentials. We also found that the photoelectrochemical etching treatment is effective to increase the gas sensitivity of ZnO gas sensor.