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

• Published in: Journal of display technology Vol. 5; no. 12; pp. 462 - 467
• Main Authors: Kamiya, T., Nomura, K., Hosono, H.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.12.2009; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• 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
• ISSN: 1551-319X; 1558-9323
• DOI: 10.1109/JDT.2009.2022064

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.