SURFACE PROCCESSING OF SEMICONDUCTOR BY THE USE OF PHOTOELECTROCHEMICAL TECHNIQUE

光电化学腐蚀是一种制备半导体表面微结构的有效方法。它直接影响光电化学活性位点，并导致半导体表面的独特形貌，这取决于晶粒结构的某些特征，例如晶体取向和晶界的存在等。研究了CdSe、SrTiO_3压敏电阻和ZnO气敏元件的光电化学腐蚀位置选择性，发现在弱阳极极化下，CdSe多晶电极的光电化学腐蚀后，晶界未溶解，晶界两侧被深度腐蚀。相反，在强阳极极化下，晶界选择性溶解。我们用半导体/电解质界面能带模型和晶界势垒解释了这种刻蚀位置选择性。晶界势垒在压敏电阻器、传感器、光电化学器件等半导体电子陶瓷器件中起着重要作用。光电化学腐蚀使人们可以直观地观察到晶界势垒结构并对其产生影响，我们将这种腐蚀技术应用于SrTiO_3压敏电阻和ZnO气敏元件。对于SrTiO_3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，光电化学腐蚀处理是有效的，以提高ZnO气敏元件的气体灵敏度。

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.