Abstract
Thin film transistor(TFTs) is the most crucial active component in flat-panel displays. With the development of display industry, there are not only the demands for miniaturization of devices, but also toward the flexible and light transmission type devices. Within these, the characteristics of channel layer such as low concentration and high mobility of carriers, are important to the performance of overall devices. Furthermore, in order to deposit on flexible substrates, the process should under low temperature because the substrates could not afford the high temperature. Although materials like amorphous silicon and also organic materials have been intensively studied in the past decades, amorphous oxide semiconductors (AOSs) made with In-Zn composite oxide has recently caught a great attention. The later has the advantages including low process temperature, relatively higher carrier mobility, and good thermal stability (Tc~6000C). In order to suppress the carrier density of the In-Zn composite oxide films, they are commonly doped with Ga. It is suspected that the role of Ga may be replaced with Al, which is obviously abundant and cheap compared to Ga. In this work, a detail electrical and optical characterization on the co-sputtered amorphous indium-aluminium-zinc oxide(IAZO) has been performed. The bandgap of materials is one of the important parameters for affecting the electrical behavior of them. Here we utilized the spectroscopic ellipsometry to analyze the properties of IAZO(In:Al:Zn=2:<<1:1) in different annealing temperatures. In this study, we found that IAZOs were amorphous when be deposited under room temperature, and would be crystallized after the post-annealing about 8500C. During the increase of annealing temperature, the carrier concentration would first decrease from 5.99×1018 cm-3 to 2×1017 cm-3 and then increase to 5.94×1018 cm-3, and the carrier mobility would raise to 14.9 cm2V-1s-1 from 2.48 cm2V-1s-1. Furthermore, the index of refractive would increase during the increase of annealing temperature, and the bandgap of materials would increase from 3.122 eV to 3.516 eV when they were crystallized.