SURFACE PROCCESSING OF SEMICONDUCTOR BY THE USE OF PHOTOELECTROCHEMICAL TECHNIQUE

光电化学刻蚀是制备半导体表面微结构的一种有用的技术。它直接影响半导体的光电化学活性中心，并根据晶体结构的某些特征，如晶体取向和晶界的存在等，导致半导体表面具有独特的形貌。研究了CdSe、SrTiO3压敏材料和氧化锌气敏元件的光电化学腐蚀位选择性，观察到在弱阳极条件下对CdSe多晶电极进行光电化学刻蚀后，晶界未被溶解，晶界两侧被深度刻蚀。相反，晶界在强阳极极化下选择性溶解。用半导体/电解液界面能带模型和晶界势垒模型解释了这种刻蚀位置的选择性。晶界势垒在压敏电阻、传感器、光电化学器件等半导体电陶瓷器件中起着重要的作用。光电化学刻蚀可以直观地观察到晶界势垒结构并对其产生影响。我们将这种刻蚀技术应用于钛酸锶压敏电阻和氧化锌气敏元件中。对于SrTiO3型压敏电阻，起始电压和电流斜率随腐蚀电位的变化而变化。我们还发现，光电化学刻蚀处理可以有效地提高氧化锌气敏元件的气敏性能。

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.