CrossRef 26. Wagner CD, Riggs WM, Davis LE, Moulder JF: Handbook of X-Ray Photoelectron Spectroscopy. Eden Prairie: Perkin-Elmer Corporation; 1979. Competing interests The authors declare that they have no competing interests. Authors’ contributions MQG and YLX designed the experiments. MQG, YB, and FX carried out the experiments and performed data analysis. MQG wrote the paper.

All authors read and approved EVP4593 the final manuscript.”
“Background High-brightness deep ultraviolet light-emitting diodes (UV LEDs) have attracted much attention in areas of air/water sterilization and decontamination, bioagent detection and natural light, identification, UV curing, and biomedical and analytical instrumentation [1]. To date, the maximum external quantum efficiency (EQE) for commercialization of deep UV LEDs is 3% at the wavelength of 280 nm [2, 3]. Various reasons can account for the poor EQE, mainly such as relatively low-resistance ohmic contacts, low hole concentration in p-type AlGaN layer, and the absence of transparent conductive PRI-724 oxides (TCOs) electrode in the deep UV wavelength region [4, 5]. In particular, it is believed that the development of high-performance TCOs electrode in the deep UV region is a key to increase the EQE of UV LEDs.

Conventionally, indium tin oxide (ITO), which exhibits high conductance and good transparency in a visible region, has been widely used as the TCOs electrodes in LEDs and solar cells [6, 7]. However, it has an opaque property in the deep UV (<300 nm) region due to a small bandgap (approximately 3.2 eV), and hence, new TCO materials need to be explored for deep UV LEDs. The wide bandgap materials such as SiO2, Si3N4, HfO2 are attractive as TCOs for deep UV LEDs because of their high transmittance in deep UV regions, but it is difficult to provide electrical conductivity into these materials. In the meantime, the gallium oxide with β phase (β-Ga2O3) having a large optical bandgap of 4.9 eV has been reported as a deep-UV TCO material [8] because its conductivity PtdIns(3,4)P2 can be improved by thermal annealing, impurity doping,

or incorporating some conducting paths using SWNTs. The Ga2O3 film has also excellent adhesion to GaN surfaces [9]. For example, since undoped Ga2O3 film has insulating properties (i.e., conductivity (σ) <10-9 Ω-1 · Cm-1), it was doped with tin (Sn) atoms to increase the conductivity at the expense of optical transmittance. For 3 mol% Sn-doped Ga2O3 films, the conductivity was increased up to 375 Ω-1 · Cm-1 (42 Ω/square) but the transmittance decreased to approximately 15% in the deep UV region (280 nm) [10]. In order to improve the low optical properties, several groups have reported synthesized TCO layer by wet-based nanoparticles (NPs), such as ITO, indium zinc oxide (IZO), antimony zinc oxide (AZO), antimony tin oxide (ATO), etc. [11–14]. This small particle size (i.e.

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