Optical characteristics of light-emitting diodes with high transparent conductive film at low temperatures

In this paper, we report the synthesis and transmittance of a titanium–indium–tin oxide (TITO) film, fabricated through a low-temperature process. The TITO film was fabricated by incorporating a 2-nm-thick titanium barrier at the bottom of an ITO film. The transmittance characteristics of the TITO film were examined for light-emitting diodes (LEDs) of various wavelengths at different post-annealing temperatures. A saturated high transmittance was observed at a temperature of 550 °C, which is relatively low when compared to that in the case of a conventional ITO film. Photoluminescence studies demonstrated that a 450-nm-thick TITO film, fabricated at 550 °C, was highly effective in improving the performance of the LED, when compared to conventional ITO films. The X-ray diffraction peaks, scanning electron microscopy images, and transmittance electron microscopy images confirmed that titanium atoms could improve the crystallization of ITO. It was found that non-crystallization in ITO was effectively activated by the titanium barrier. Furthermore, the optical bandgap (3.77 eV for the conventional ITO film) was improved to 3.92 eV in the TITO film. An infrared LED fabricated with a TITO film displayed 70% higher light output power than that with a conventional ITO film. These results suggest that using a titanium barrier is essential to effectively improve inactive nucleation sites in ITO films grown at low temperatures.