Effect of Absorber Composition on Ultra-violet Light Block Enhancement in Sunscreen via Quantum-Dot Ultra-violet CMOS Image Sensor

Abstract

As the commonly used Si CMOS image sensors have theoretical limitations which is that the quantum efficiency of Si-based photo-detector is low under the 400-nm of UV wavelength, many researchers tried to enhance the quantum efficiency of the UV wavelengths using wide bandgap materials (ZnO, TiO2, IGZO, etc.). However, these technologies are difficult to be commercialized because of higher-priced materials and fabrication complexity which directly lead to the cost increment of devices. In this study, we applied the quantum-dots on the Si-based CMOS image sensor (QD CIS) to selectively sense under 400-nm-wavelength of the UV light without any wide bandgap materials. Therefore, we can visualize the UV light that the general Si CMOS image sensor or human eyes are impossible to sense. To evaluate the UV-sensing QD CIS, we investigated the effects of sunscreen applied on human skin which are really close to our living. Generally, the sunscreens consist of materials that absorb or reflect the UV lights. The absorption coefficient and material bandgap were measured by spectroscopic ellipsometry to evaluate the compositions of the sunscreen respectively. Particularly, we analyzed the bandgap of each material of the unknown mixture composing the sunscreen and compared those materials with the UV pixel intensity of the image captured by the quantum-dot CMOS image sensor. As a result, UV-B absorber shows the highest total absorption amount in a value of 725,693 a.u. measured by spectroscopic ellipsometry with the highest UV pixel intensity with 6.67 a.u. which indicates the correlation between the absorption coefficient of the sunscreen measured by spectroscopic ellipsometry and the UV-light intensity of the image captured by QD CIS. Thus, the QD CIS illustrated the potential application for the high-sensitivity of UV light using the Si CMOS image sensor with quantum-dots, which could photograph and analyzed the UV illumination by simply capturing UV images.