High-Sensitivity Image Sensors Overlaid With Thin-Film Gallium Oxide/Crystalline Selenium Heterojunction Photodiodes

We developed a stacked CMOS image sensor overlaid with a thin-film gallium oxide (Ga
₂
O
₃
)/crystalline selenium (c-Se) heterojunction photodiode. Uniform c-Se films laminated on the CMOS circuits were fabricated through a low-temperature (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 the image sensors by adjusting the thickness of the c-Se films. Therefore, we herein present the first high-resolution 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 Ga
₂
O
₃
film as a high hole-injection barrier.