Abstract
In this paper, we studied a p-type reflector based on indium tin oxide (ITO) for vertical-type ultraviolet light-emitting diodes (UV LEDs). We investigated the reflectance properties with different deposition methods. An ITO layer with a thickness of 50 nm was deposited by two different methods, sputtering and e-beam evaporation. From the measurement of the optical reflection, we obtained 70% reflectance at a wavelength of 382 nm by means of sputtering, while only 30% reflectance resulted when using the e-beam evaporation method. Also, the light output power of a $1mm{\times}1mm$ vertical chip created with the sputtering method recorded a twofold increase over a chip created with e-beam evaporation method. From the measurement of the root mean square (RMS), we obtained a RMS value 1.3 nm for the ITO layer using the sputtering method, while this value was 5.6 nm for the ITO layer when using the e-beam evaporation method. These decreases in the reflectance and light output power when using the e-beam evaporation method are thought to stem from the rough surface morphology of the ITO layer, which leads to diffused reflection and the absorption of light. However, the turn-on voltage and operation voltage of the two samples showed identical results of 2.42 V and 3.5 V, respectively. Given these results, we conclude that the two ITO layers created by different deposition methods showed no differences in the electric properties of the ohmic contact and series resistance.
