Microfabrication of Semiconductor Surface by Photoelectrochemical Etching Technique

在硫酸溶液中对TiO_2电极进行光电化学腐蚀（光刻），得到纳米结构的表面（称为“纳米蜂窝”结构）。另一个有趣的发现是其潜在的依赖性蚀刻位点选择性，即，在弱阳极极化（向上能带弯曲）条件下，烧结颗粒TiO_2电极的颗粒体发生优先光电化学溶解，形成仅由晶界组成的“骨架”结构。后者必须提供一个可能性的表征晶界，这是众所周知的，在一些陶瓷器件中发挥着至关重要的作用。在本工作中，我们报告了更详细的表征烧结颗粒TiO_2的晶界以及“纳米蜂窝”的尺寸控制。改变光刻时间、光刻电位和光强等光刻条件并不改变“纳米蜂窝”的大小，表明其大小反映了所用TiO_2的本征性质。实际上，通过在氢气气氛中还原TiO_2，提高TiO_2电极的施主密度，可以减小“纳米蜂窝”的尺寸。对于施主密度为10 μ cm ~ 2量级的TiO_2电极<21><-3>，其尺寸为30 nm。这种精细结构的形成将在各种器件如（光）催化剂、传感器和染料敏化太阳能电池中找到有用的应用。

The photoelectrochemical etching (photoetching) of a TiO_2 electrode in sulfuric acid solution generates nano-structured surface (named "nano-honeycomb" structure). Another interesting finding is its potential dependent etching site selectivity, i.e., a preferential photoelectrochemical dissolution of grain bulk for a sintered pellet TiO_2 electrode under weak anodic polarization (upward band bending), which results in the formation of a "skeleton" structure consisting of only grain boundaries. The latter must offer a possibility of characterize grain boundaries, which are known to play a crucial role in some ceramic devices.In the present work, we report more detailed characterization of grain boundary of a sintered pellet TiO_2 as well as the size control of the "nano-honeycomb". Varying the photoetching conditions such as photoetching time, photoetching potential and light intensity did not change the size of a "nano-honeycomb", suggesting that its size is a reflection of the intrinsic property of the TiO_2 used. Modifying the properties of TiO_2 would change it. Actually upon increasing the donor density of a TiO_2 electrode by reducing it in H_2 atmosphere, the size of the "nano-honeycomb" decreased. For a TiO_2 electrode with a donor density of the order of 10^<21> cm^<-3>, the size amounts to 30 nm. The formation of such a fine structure will find useful applications to various devices such as (photo) catalysts, sensors and dye-sensitized solar cells.