National Centre for Nanotechnology, Department of Chemical and Materials Engineering, Pakistan Institute of Engineering and Applied Sciences, Islamabad 45650, Pakistan.
J Colloid Interface Sci. 2010 Mar 1;343(1):271-80. doi: 10.1016/j.jcis.2009.11.045. Epub 2009 Nov 26.
Multilayer TiO(2)-Ge thin films have been deposited using electron beam evaporation and resistive heating. The thickness of the TiO(2) layers is 20 nm, while the thickness of the Ge layers varies from 2 to 20 nm with a step of 2 nm away from the substrate. These films were characterized by studying their optical, electrical, and structural properties. The films were annealed at various temperatures up to 500 degrees C for 2 h. The films are amorphous up to an annealing temperature of 400 degrees C, although Raman spectra suggest short-range ordering (and adjustments). The films annealed at 450 and 500 degrees C exhibit X-ray reflections of Ge and anatase TiO(2). Illumination in sunlight increases the conductivity of the as-deposited and annealed films. The band gap of the amorphous films changes from 1.27 to 1.41 eV up to 400 degrees C; the major contribution is possibly through direct transition. Two band gap regimes are clearly seen after 450 and 500 degrees C, which have been assigned to an indirect band gap at about 1.2 eV and a direct band gap at about 1.8 eV. Conductivity of the multilayer films has been higher than that of pure Ge film. The conductivity increases with annealing temperature with abrupt increase at about 380 degrees C. The results imply that the TiO(2)-Ge multilayer films may be employed as heterojunctions with tunable band gap energy as related to quantum confinement effects.
采用电子束蒸发和电阻加热的方法沉积了多层 TiO(2)-Ge 薄膜。TiO(2)层的厚度为 20nm，而 Ge 层的厚度从 2nm 到 20nm 不等，每隔 2nm 离开基底。通过研究这些薄膜的光学、电学和结构性能对其进行了表征。这些薄膜在各种温度下退火，最高可达 500°C，持续 2 小时。在 400°C 以下的退火温度下，薄膜为非晶态，尽管拉曼光谱表明存在短程有序（和调整）。在 450°C 和 500°C 下退火的薄膜表现出 Ge 和锐钛矿 TiO(2)的 X 射线反射。在阳光下照射会增加未退火和退火薄膜的电导率。非晶态薄膜的能带隙从 1.27eV 变化到 1.41eV，最高可达 400°C；主要贡献可能是通过直接跃迁。在 450°C 和 500°C 之后，明显出现了两个能带隙区域，分别为约 1.2eV 的间接能带隙和约 1.8eV 的直接能带隙。多层薄膜的电导率高于纯 Ge 薄膜。电导率随退火温度的升高而升高，在约 380°C 时急剧增加。结果表明，TiO(2)-Ge 多层薄膜可用作能带隙能量可调谐的异质结，与量子限制效应有关。
