Monolithic integration of graphene and lithium niobate layer grown by atomic layer deposition for uncooled infrared photodetectors

Graphene-based hybrid structures offer a promising platform to enhance device performance via unique phenomena such as the photogating effect. Lithium niobate (LiNbO3) has excellent optoelectronic properties, including pyroelectric, piezoelectric, electro-optic, and nonlinear optical characteristics, and is a promising pyroelectric photosensitizer for graphene infrared detectors. However, bulk LiNbO3 restricts the monolithic integration of devices onto complementary metal–oxide–semiconductor (CMOS) chips. In this work, we overcome that by employing an atomic layer deposition (ALD)-grown LiNbO3 thin film on a silicon substrate, a CMOS-compatible approach. This study presents the fabrication of an uncooled long-wavelength infrared (LWIR) graphene photodetector monolithically integrated with an ALD-grown LiNbO3 on a silicon substrate. The O3-assisted ALD process was investigated to achieve the minimum thickness required crystalline LiNbO3 growth at temperatures below 400 °C. Successful growth was confirmed by X-ray diffraction analysis and Auger electron spectroscopy. The device, comprising graphene field effect transistors with the ALD-grown LiNbO3 photosensitizer layer, exhibited a clear photoresponse under irradiation by 8.0 and 10.5 μm LWIR light, with maximum responsivities of 95.9 and 187 kV/W, respectively. These findings contribute to the development of high-performance uncooled monolithic IR image sensors.