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 like the photogating effect. Lithium niobate (LiNbO3), with its excellent optoelectronic properties, including pyroelectric, piezoelectric, electro-optic, and non-linear optical characteristics, is a promising pyroelectric photosensitizer for graphene infrared detectors. However, using bulk LiNbO3 restricts the monolithic integration of devices onto complementary metal-oxide-semiconductor-based chips. In this work, we overcome that by employing an 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 via ALD-grown LiNbO3 on a silicon substrate through atomic layer deposition (ALD). The O3-assisted ALD process was investigated to achieve the minimum required crystalline LiNbO3 layers at temperatures below 400 {degree sign}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 μm and 10.5 μm LWIR light, with maximum responsivities of 95.9 kV/W and 187 kV/W, respectively. These findings contribute to the development of high-performance uncooled monolithic IR image sensors.