Transparent conducting oxide semiconductors for transparent electrodes

Abstract

The present status and prospects for further development of polycrystalline or amorphous transparent conducting oxide (TCO) semiconductors used for practical thin-film transparent electrode applications are presented in this paper. The important TCO semiconductors are impurity-doped ZnO, In 2 O 3 and SnO 2 as well as multicomponent oxides consisting of combinations of ZnO, In 2 O 3 and SnO 2 , including some ternary compounds existing in their systems. Development of these and other TCO semiconductors is important because the expanding need for transparent electrodes for optoelectronic device applications is jeopardizing the availability of indium-tin-oxide (ITO), whose main constituent, indium, is a very expensive and scarce material. Al-and Ga-doped ZnO (AZO and GZO) semiconductors are promising as alternatives to ITO for thin-film transparent electrode applications. In particular, AZO thin films, with a low resistivity of the order of 10 −5 cm and source materials that are inexpensive and non-toxic, are the best candidates. However, further development of the deposition techniques, such as magnetron sputtering or vacuum arc plasma evaporation, as well as of the targets is required to enable the preparation of AZO and GZO films on large area substrates with a high deposition rate.

Graphene photonics and optoelectronics

“…ITO has strong absorption above 4eV due to interband transitions 76 , with other features at lower energy related to scattering of free electrons with Sn atoms or grain boundaries 76 . ITO is commercially available with T∼ 80% and R s as low as 10Ω/ on glass 83 , and ∼ 60 − 300Ω/ on polyethylene terephthalate (PET) 84 . Note that T is typically quoted at 550nm, since this is where the human eye spectral response is maximum 76 .…”

Free-carrier absorption in transparent conducting oxides: Phonon and impurity scattering inSnO2

“…They are used in applications ranging from solar cells, displays, smart windows, and touch screens to light-emitting diodes. [1][2][3][4] In TCOs such as In 2 O 3 , SnO 2 , and ZnO, the energy at which absorption of photons can lead to excitation of electrons from the valence band into the conduction band) is above the visible region. What is often overlooked in the consideration of the transparency criterion is that the free carriers that need to be present to ensure high conductivity can also absorb photons.…”

Overview of electroceramic materials for oxide semiconductor thin film transistors

“…The key binary oxide semiconductors (ZnO, In 2 O 3 , SnO 2 , and TiO x etc.) of interest have wide band gaps (>3.0 eV) that allow the transmission of visible light [13]. Often even when undoped, they exhibit much higher electrical conductivities (10 −2 Ω −1 cm −1 to 10 2 Ω −1 cm −1 ) than other wide gap metaloxide materials due to inherent high levels of n-type conductivity.…”