Evaluation of Sub-Gap States in Amorphous In-Ga-Zn-O Thin Films Treated with Various Process Conditions
- PDF / 291,694 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 9 Downloads / 135 Views
Evaluation of Sub-Gap States in Amorphous In-Ga-Zn-O Thin Films Treated with Various Process Conditions Kazushi Hayashi, Aya Hino, Hiroaki Tao, Yasuyuki Takanashi, Shinya Morita, Hiroshi Goto, and Toshihiro Kugimiya Electronics Research Laboratory, Kobe Steel, Ltd., 1-5-5 Takatsuka-dai, Nishi-ku, Kobe, 6512271, Japan. ABSTRACT In the present study, the sub-gap states of amorphous In-Ga-Zn-O (a-IGZO) thin films treated with various process conditions have been evaluated by means of capacitance-voltage (CV) characteristics and isothermal capacitance transient spectroscopy (ICTS). It was found that the space-charge densities of the a-IGZO decreased as the oxygen partial pressure was increased during the sputtering of a-IGZO thin films. The ICTS spectra for the 4, 8, and 12 % samples were similar and the peak positions were found to be around 1 10-2 s at 180 K. On the other hand, the peak position for the 20 % sample shifted to a longer time regime and was located at around 2 10-1 s at 180 K. The total densities of the traps for the 4, 8, and 12 % samples were calculated to be 56 × 1016 cm-3, while that for 20 % was one order of magnitude lower than the others. From Thermal desorption spectrometer, it was found that desorption of Zn atoms started at a temperature higher than 300 °C for the 4 % sample, while desorption of Zn was not observed for the 20 % sample. The introduction of the sub-gap states could be attributed to oxygen-rich and/or Zn-deficient defects in the a-IGZO thin films formed during thermal annealing. INTRODUCTION It is widely recognized that oxide semiconductors such as amorphous In-Ga-Zn-O (aIGZO) are promising channel materials for thin-film transistors (TFTs) in next generation flat panel display since they have a higher electron mobility than conventional materials like amorphous Si [1,2]. A crucial issue for realization of practical TFTs is comprehension of their electronic properties, information especially regarding sub-gap states in the a-IGZO thin films that govern the TFT performance. The nature of the sub-gap states such as their density and activation energy should be clarified since it is varied depending on the fabrication process and parameters. Isothermal capacitance transient spectroscopy (ICTS), in which the capacitance transient response originated from an emission of captured carriers is measured under isothermal conditions, is a highly sensitive and spectroscopic technique to directly determine the energy level and the density of carrier traps [3-5]. In the present study, capacitance-voltage (C-V) characteristics and ICTS measurements were applied to evaluate the sub-gap states in the aIGZO thin films treated with various processes. The influence of the oxygen partial pressures during the a-IGZO sputtering on the electronic properties of the a-IGZO thin films was discussed. EXPERIMENTAL
55
A series of metal oxide semiconductor (MOS) diodes with bottom gate structure was fabricated for evaluation. Mo thin films that act as gate electrodes were deposited on glass substrates b
Data Loading...
