This improvement may be attributed to the reduced optical light scattering via undoped Ga2O3 NPs (<15 nm in diameter). On the other
hand, the transmittance was decreased by 8.4% due to the optical loss by SWNTs after one dipping; however, it is still good enough to use in the deep UV region as well as visible region [22]. By comparison, the transmittances of oxide-based TCOs were reported to be lower than 40% at 280 nm [23, 24] while those of the immersing electrodes such as SWNT, graphene, and Ag nanowire thin films were approximately 70% at 280 nm [25]. Figure 6 Optical transmittance spectra of undoped Ga 2 O 3 film, Ga 2 O 3 NP layer, and Ga 2 O 3 NP/SWNT layer deposited on quartz. Under 15 times of dipping in SWNT-dispersed solution. In order to Galunisertib solubility dmso determine the optimal transmittance for SWNT solution dipping times, Figure 7 KU55933 shows the relationship between the transmittance at 280 nm and SWNT solution dipping times. The optical transmittance is reduced with increasing the dipping times. That is, the transmittance values were 85.4%, GSK461364 80.5%, 79.0%, 77.0%, 52.7%, and 18.6% after dipping treatments of 0, 5, 10, 15, 20, and 25 times, respectively. The reduction ratio of the transmittance is not so great (5% to 8%)
for 0 to 15 dipping time ranges. For example, 15 times of dipping samples show a slight decrease in the transmittance due to the coverage with SWNTs on the undoped Ga2O3 NP layer, but a remarkable influence on the reduction of the
transmittance, whereas it provided pronounced enhancement effect in electrical conductivity, as shown in Figure 5. From these results, we can conclude that our proposed TCO scheme of the Ga2O3 NP/SWNT layer may be useful as an electrode for deep UV LEDs. However, the resistivity of Ga2O3 NP/SWNT layer is approximately 3 orders higher in magnitude than that observed for commercial ITO films [26], and should be further reduced by introducing doped Ga2O3 NPs without transmittance loss. Figure 7 Optical Methane monooxygenase transmittance versus SWNT solution dipping times measured for the Ga 2 O 3 NP/SWNT layer. Conclusions We proposed and investigated the electrical and optical properties of undoped Ga2O3 NP layer combined with SWNTs by using the simple spin and dip-coating methods for deep UV LEDs. From the I-V curve characteristics, the Ga2O3 NP/SWNT layer showed a high current level of 0.4 × 10-3 A at 1 V. Compared with the undoped Ga2O3 NP layer, optical transmittance of Ga2O3 NPs/SWNT layer after 15 times of dipping was decreased by only 15% at 280 nm. By adjusting the dipping times in the Ga2O3 NP/SWNT layer, we obtained improved optical transmittance of 77.0% at 280 nm after 15 times of dip-coating processes. Acknowledgements This work was supported by the National Research Foundation of Korea (NRF) Grant funded by the Korean government (No. 2011–0028769). References 1.