![]() The Ge/Si photodiode consists of a 300 nm Si layer, n-type doped with phosphorus (P) to a concentration of 1 × 10 19 cm –3, followed by a 1 μm thick intrinsic Ge layer. (7,8) In addition, many materials and solvents are opaque under VIS illumination, but transparent in the SWIR range or, on the contrary, they are transparent in the VIS but feature intense absorption bands in the SWIR. (6) Improving the current machine vision systems is of critical importance for aircraft landing, drone inspection, and self-driving cars. (3−5) Since Rayleigh scattering on small particles is proportional to λ –4, when compared to VIS, SWIR features longer penetration depths in high scattering media, such as rain, fog, or smoke, thus enabling enhanced visibility in severe weather conditions, estimation of distance and localization of obstacles. (1,2) These regions of the electromagnetic spectrum provide a wealth of information not accessible to cameras operating in the visible range (VIS, λ = 380–750 nm), which is extremely relevant for autonomous driving, security, medical, and environmental monitoring applications. The development of optical devices operating in the near-infrared (NIR: λ = 750–1400 nm) and short-wave infrared (SWIR, λ = 1400–2500 nm) spectral ranges is experiencing a strong renaissance driven by Internet of Things (IoT) and Artificial Intelligence of Things (AIoT) applications. The continuous voltage tuning, combined with the nonlinear photoresponse of the detector, enables a novel approach to spectral analysis, demonstrated by identifying the wavelength of a monochromatic beam. The possibility of detecting two spectral bands with the same pixel opens up interesting applications in the field of IR imaging and material recognition, as shown in a solvent detection test. The photoresponse can be switched by inverting the bias polarity between the near and the short-wave IR bands, with specific detectivities of 1.9 × 10 10 and 4.0 × 10 9 cm The device is obtained from a vertical GeSn/Ge/Si stack, forming a double junction n-i-p-i-n structure, epitaxially grown on a Si wafer. Here, we present a two-terminal dual-band detector, which provides a bias-switchable spectral response in two distinct IR bands. Infrared (IR) multispectral detection is attracting increasing interest with the rising demand for high spectral sensitivity, room temperature operation, CMOS-compatible devices.
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