Structure and Electronic Properties of Crystalline and Amorphous Zinc Indium Tin Oxide Thin Films

The local structures and surface electronic properties of crystalline (c-) and amorphous (a-) Zn and Sn codoped In2O3 (ZITO) films were studied. X-ray absorption spectroscopy (XAS) measurements confirm that Zn and Sn dopants occupy In sites in the bixbyite structure of c-ZITO. Also, Zn dopants are generally under-coordinated and some compensated Sn dopants are over-coordinated, as demonstrated by the trend in coordination numbers (CN) of CNSn>CNIn>CNZn. Aliovalent Sn dopants form Frank-Kostlin clusters, &parl0;2Sn•InO'' i&parr0;x , which can act as donors when reduced.;XAS and anomalous X-ray scattering studies on a-ZITO show that the local structure in a-ZITO is somewhat different than that in c-ZITO, particularly around Zn. The Zn-O bond length is significantly smaller than in c-ZITO and Zn is 4-fold coordinated. The smaller coordination numbers in a-ZITO follow the same trend as in c-ZITO. Unlike in c-ZITO, variations in the Sn/Zn ratio do not alter the electrical properties of a-ZITO, although variations in deposition oxygen pressure do. The 3-D geometrical arrangement linking local structure units seems to play a key role in charge balancing ZITO.;As measured by in situ grazing incidence wide angle X-ray scattering, ZITO crystallizes at a higher temperature than In2 O3 and Sn-doped In2O3. The difference is attributed to a higher activation energy, which may result from the unique structure around Zn in a-ZITO. Increasing the codoping level consistently increases crystallization temperature. For a given codoping level, the crystallization temperature during deposition is lower than that during post-deposition annealing.;X-ray and ultraviolet photoelectron spectroscopy measurements show that a-ZITO and c-ZITO thin films have similar surface electronic properties. In situ a-ZITO and c-ZITO films have low ionization potentials that are similar to In2O3. However, dry-air-annealed in situ films, ex situ films, and bulk ceramics have higher ionization potentials that are similar to ITO and match well with previous results on air-exposed surfaces. Lastly, a parallelogram plot of work function versus Fermi level shows that a wider range of work functions is achievable in ZITO materials than in Sb-doped SnO2, Al-doped ZnO, and Sn-doped In2O3.