This article reviews optoelectronic devices based on graphene and related two-dimensional (2D) materials. The review includes basic considerations of process technology, including demonstrations of 2D heterostructure growth, and comments on the scalability and manufacturability of the growth methods. We then assess the potential of graphene-based transparent conducting electrodes. A major part of the review describes photodetectors based on lateral graphene p-n junctions and Schottky diodes. Finally, the progress in vertical devices made from 2D/3D heterojunctions, as well as all-2D heterostructures is discussed.

Few-layer molybdenum disulfide (FL-MoS2) films have been integrated into amorphous silicon (a-Si:H) pin photodetectors. To achieve this, vertical a-Si:H photodiodes were grown by plasma-enhanced chemical vapor deposition on top of large-scale synthesized and transferred homogeneous FL-MoS2. This novel detector array exhibits long-term stability (more than six month) and outperforms conventional silicon-based pin photodetectors in the infrared range (IR, λ = 2120 nm) in terms of sensitivities by up to ~50 mAW-1. Photodetectivities of up to ~2∙10^10 Jones and external quantum efficiencies of ~3 % are achieved. The detectors further feature the additional functionality of bias-dependent responsivity switching between the different spectral ranges. The realization of such scalable detector arrays is an essential step towards pixelated and wavelength-selective sensors operating in the IR spectral range.

A large and growing number of applications benefit from simple, fast and highly sensitive 3D imaging sensors. The Focus-Induced Photoresponse (FIP) can achieve 3D sensing functionalities by simply evaluating the irradiance dependent nonlinear sensor response in defect-based materials. Since this advantage is intricately associated to a slow response, the electrical bandwidth of present FIP detectors is limited to a few $${\text{kHz}}$$kHz only. The devices presented in this work enable modulation frequencies of 700 kHz and beat frequency detection up to at least 3.8 MHz, surpassing the bandwidth of reported device architectures by more than two orders of magnitude. The sensors achieve a SNR of at least $$\sim 53\;{\text{dB}}$$∼ 53 dB at $$115\;{\text{cm}}$$115 cm and a DC FIP detection limit of 0.6 µW/mm². The mature and scalable low-temperature a-Si:H process technology allows operating the device under ambient air conditions waiving additional back-end passivation, geometrical fill factors of $$100\%$$100 % and tailoring the FIP towards adjustable 3D sensing applications.

A large and growing number of applications benefit from innovative and powerful 3D image sensors. Graphene photodetectors can achieve 3D sensing functionalities by intrinsic optoelectronic frequency mixing due to the nonlinear output characteristics of the sensor. In first proof of principle distance measurement demonstrations, we achieve modulation frequencies of 3.1 MHz, signal-to-noise ratios of ∼40 dB, distance detection up to at least 1 m, and a mean accuracy of 25.6 mm. The scalable More than Moore detector approach enables geometrical fill factors close to 100% and can easily complement powerful functionalities by simple back-end integration on top of CMOS electronics.

Photodetectors operating at the wavelength in the visible spectrum are key components in high-performance optoelectronic systems. In this work, massive nonlinearities in amorphous silicon p-i-n photodiodes enabled by the photogating are presented, resulting in responsivities up to 744 mA/W at blue wavelengths. The detectors exhibit significant responsivity gains at optical modulation frequencies exceeding MHz and a more than 60-fold enhanced spectral response compared to the non-gated state. The detection limits down to 10.4 nW/mm ² and mean signal-to-noise ratio enhancements of 8.5 dB are demonstrated by illuminating the sensor with an additional 6.6 µW/mm ² red wavelength. Electro-optical simulations verify photocarrier modulation due to defect-induced field screening to be the origin of such high responsivity gains. The experimental results validate the theory and enable the development of commercially viable and complementary metal oxide semiconductor (CMOS) compatible high responsivity photodetectors operating in the visible range for low-light level imaging and detection.