High-Sensitivity Image Sensors Overlaid With Thin-Film Gallium Oxide/Crystalline Selenium Heterojunction Photodiodes
Abstract: We developed a stacked CMOS image sensor overlaid with a thin-film gallium oxide (Ga2O3)/crystalline selenium (c-Se) heterojunction photodiode. Uniform cSe films laminated on the CMOS circuits were fabricated through a lowtemperature (200 °C) tellurium-diffused crystallization process. This stacking structure has several advantages, such as a high aperture ratio, low crosstalk, and high sensitivity. We successfully controlled the size of the polycrystalline particles to much smaller than the pixel size of theimage sensors by adjusting the thickness of the c-Se films. Therefore, we herein present the first highresolution images obtained with such a device. Furthermore, the dark current, which is induced by the carrier injection from an external electrode, was significantly reduced by employing a wide bandgap Ga2O3 film as a high holeinjection barrier.