Correlated Metals Transparent Conductors with High UV to Visible Transparency on Amorphous Substrates

Abstract

strategy for conventional transparent conducting oxides (TCOs) is to resort to degenerately dope wide-bandgap semiconductors to achieve the two key properties: electrical conductivity and optical transparency. Wide bandgap semiconductors are selected as host materials, which have the interband transitions above the visible spectrum, whereas dopants increase carrier density and thus electrical conductivity. Tin-doped indium oxides (ITOs) have been widely used because of its best balance of high electrical conductivity and optical transparency in the visible spectrum. [3] However, the increasing use of ITO as TCOs has resulted in the increase in the cost of ITO due to the limited availability of indium ore. [4] Meanwhile, many other applications, such as solar blind detection, ultraviolet (UV) lithography, UV light-emitting diodes, and UV curing, require transparent conductors in the UV spectrum. [5][6][7][8] However, conventional TCOs with high conductivity present low transmittance on the UV side of the spectrum. [1] Recently, an alternative design strategy has been proposed to use correlated metals with the intrinsic high carrier density exhibiting strong electron correlations to achieve both high electrical conductivity, thus low resistivity, and optical transparency in the UV-visible spectral range, overcoming the limitations of conventional TCOs. [9][10][11][12][13][14][15][16][17][18][19] It has been shown that as correlated metal films on single crystal substrates get thin, they maintain low resistivity and thus low sheet resistance at room temperature (RT) whereas their optical transmittance is comparable to (or higher than) conventional TCOs in the visible (or UV) spectrum. [9,10,17] However, the epitaxy so far required expensive and size-limited single crystal substrates, which impedes the application of correlated metals as TCOs.Meanwhile, oxide nanosheets drew attention because they can be used as buffer layers to promote the growth of highquality and thus high-performance transition metal oxide films regardless the supporting substrates. [20][21][22][23][24][25][26] Almost full coverage of oxide nanosheets can be obtained on virtually any flat substrates without the limitation of the substrate size by using Langmuir-Blodgett method. [21,24,25] Boileau et al. showed that correlated CaVO 3 and SrVO 3 (SVO) films with a thickness of 40 nm on Ca 2 Nb 3 O 10 (CNO) nanosheets on glass had the RT Correlated metals with high carrier density and strongly correlated electron effects provide an alternative route to achieve transparent conducting materials, different from the conventional degenerately doped wide-bandgap transparent conducting oxides (TCO). The extremely low electrical resistivity and high optical transparency in the ultraviolet-visible spectral range shown in 4d correlated metals present an advantage over conventional TCOs. However, most of the 4d correlated metals are grown epitaxially on single crystal substrates. Here, it has been shown that Ca 2 Nb 3 O 10 nanosheets with different buffer laye...