The heterojunction effects of TiO2 nanotubes fabricated by atomic layer deposition on photocarrier transportation direction

Yung-Huang Chang,Chih Chen,Hsyi-En Cheng,Chien-Min Liu

doi:10.1186/1556-276x-7-231

Abstract

The heterojunction effects of TiO2 nanotubes on photoconductive characteristics were investigated. For ITO/TiO2/Si diodes, the photocurrent is controlled either by the TiO2/Si heterojunction (p-n junction) or the ITO-TiO2 heterojunction (Schottky contact). In the short circuit (approximately 0 V) condition, the TiO2-Si heterojunction dominates the photocarrier transportation direction due to its larger space-charge region and potential gradient. The detailed transition process of the photocarrier direction was investigated with a time-dependent photoresponse study. The results showed that the diode transitioned from TiO2-Si heterojunction-controlled to ITO-TiO2 heterojunction-controlled as we applied biases from approximately 0 to -1 V on the ITO electrode.

Highlights

In recent years, nanostructure materials have attracted much interest due to their remarkable physical and chemical properties
To deposit the TiO2 nanostructure by atomic layer deposition (ALD), Si substrates with the anodic aluminum oxide (AAO) templates were first placed into a quartz tube reactor with the operating environment maintained at 1.6 × 10-1 Torr and 400°C
The AAO template was selectively removed by a 0.1 wt% sodium hydroxide solution, and TiO2 nanotube arrays were fabricated on the Si substrate

Summary

Introduction

Nanostructure materials have attracted much interest due to their remarkable physical and chemical properties. Among these nanostructure materials, TiO2 nanostructures have emerged as one of the most promising materials for optoelectronic devices because of the variety of growth methods and their high melting point (1,855°C), chemical inertness, physical stability, indirect band gap (3.2 eV), high photoconversion efficiency, and photostability. Based on its excellent optical properties, TiO2 has been utilized for many applications, such as photoelectrochemical water splitting [1], photoelectrochemical generation of hydrogen [2], dye-sensitized solar cells [3], and photocatalysis [4]. The inherent high band gap of 3.2 eV limits the optical application of TiO2. In addition to modifying material properties, it is essential to understand and pay special attention to heterojunctions in the study of traditional semiconductors because the heterojunction effect

Methods

Results

Conclusion