Density of states of amorphous In-Ga-Zn-O from electrical and optical characterization

We have developed a subgap density of states (DOS) model of amorphous In-Ga-Zn-O (a-IGZO) based on optical and electrical measurements. We study the optical absorption spectrum of the a-IGZO using UV-Vis spectroscopy. Together with the first-principles calculations and transient photoconductance spe...

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Bibliographic Details
Published in:Journal of applied physics 2014-10, Vol.116 (15)
Main Authors: Yu, Eric Kai-Hsiang, Jun, Sungwoo, Kim, Dae Hwan, Kanicki, Jerzy
Format: Article
Language:English
Subjects:
Absorption spectra
Applied physics
Computer simulation
Conduction bands
Density of states
Electrical measurement
Electrical properties
First principles
Indium gallium zinc oxide
Mathematical models
Optical properties
Semiconductor devices
Spectrum analysis
Thin film transistors
Valence band
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Summary:We have developed a subgap density of states (DOS) model of amorphous In-Ga-Zn-O (a-IGZO) based on optical and electrical measurements. We study the optical absorption spectrum of the a-IGZO using UV-Vis spectroscopy. Together with the first-principles calculations and transient photoconductance spectroscopy from the literature, we determine that the valence band tail and deep-gap states are donors and can be described by exponential and Gaussian distributions, respectively. The conduction band tail and deep-gap states are examined using multi-frequency capacitance-voltage spectroscopy on a-IGZO thin-film transistors (TFTs). The extracted conduction band DOS are fitted to exponential (bandtail) and Gaussian (deep-gap) functions and their validity are supported by the activation energy vs. gate-source bias relationship of the a-IGZO TFT. The PL deep-level emission, which is almost identical to the conduction band deep-gap Gaussian, suggests that these states should be assigned as acceptors. The donor/acceptor assignments of subgap states are consistent with the 2D numerical TFT simulations.
ISSN:0021-8979
1089-7550
DOI:10.1063/1.4898567