Electronic Structures Above Mobility Edges in Crystalline and Amorphous In-Ga-Zn-O: Percolation Conduction Examined by Analytical Model

Electronic structures and carrier transport mechanisms in disordered oxide semiconductors, crystalline InGaO 3 (ZnO) m ( m = 1, 5) (c-IGZO) and amorphous InGaZnO 4 (a-IGZO), are examined based on a percolation conduction model. Donor levels ( E d ) and densities ( N D ) are estimated by numerical ca...

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Bibliographic Details
Published in:Journal of display technology 2009-12, Vol.5 (12), p.462-467
Main Authors: Kamiya, T., Nomura, K., Hosono, H.
Format: Article
Language:English
Subjects:
Amorphous materials
Amorphous structure
Amorphous-oxide semiconductor (AOS)
Analytical models
Atomic layer deposition
Crystallization
Density
Density measurement
Electron mobility
Electronic structure
Equations
Hall effect
Mathematical analysis
Mathematical models
Percolation
percolation conduction
potential barrier
Potential barriers
Semiconductors
Studies
Temperature dependence
Temperature distribution
Zinc oxide
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Summary:Electronic structures and carrier transport mechanisms in disordered oxide semiconductors, crystalline InGaO 3 (ZnO) m ( m = 1, 5) (c-IGZO) and amorphous InGaZnO 4 (a-IGZO), are examined based on a percolation conduction model. Donor levels ( E d ) and densities ( N D ) are estimated by numerical calculations of free electron densities ( n e ) obtained by Hall measurements. It shows that the donor levels are rather deep, ~0.15 eV for c-IGZO and ~0.11 eV for a-IGZO. This analysis indicates that use of a simple analytical relation of ne prop exp(- Ed /2 kT ) can not always be used to estimate E d and N D even for a low n e film because the film can be in the saturation regime at room temperature if E d and N D are small, which is actually the case for a-IGZO. The temperature dependences of electron mobilities are analyzed using an analytical equation of the percolation conduction model, which reveals that distributed potential barriers exist above mobility edges in IGZO with average heights 30-100 meV and distribution widths 5-20 meV, which depend on atomic structure and deposition condition of IGZO films. High-quality a-IGZO films have the lowest potential barriers among the IGZO films examined, in spite that a-IGZO has a more disordered amorphous structure than c-IGZO have. It is explained by the partly disordered structure of c-IGZO.
ISSN:1551-319X
1558-9323
DOI:10.1109/JDT.2009.2022064