Integrated waveguide photodetectors for visible light
In a paper published in Nature Communications, scientists at the Max Planck Institute of Microstructure Physics, Halle have demonstrated broadband, high-efficiency silicon nitride-on-silicon waveguide photodetectors that are monolithically integrated with visible light photonic circuits.
Photonic integrated circuits (PICs) are microchips that manipulate light at the micrometer and nanometer length scales. They are often designed for and used in the infrared wavelengths for fiber optic communications. Poon’s department has been developing PICs that are made with microelectronics processes in a foundry that operate at shorter wavelengths, in the visible spectrum. Visible-light PICs can transform emerging applications in sensing, displays, quantum technology, and neurotechnology by miniaturizing the components into microchips. In this paper, Poon’s team reports an efficient photodetector for PICs that operates broadly across the visible spectrum - from blue to red light. Photodetectors, which convert optical signals into electrical signals, are essential building blocks in PICs. This demonstration shows that it is possible to form good performance photodetectors with PICs. The simple fabrication process and high efficiency make the photodetectors attractive for visible spectrum PICs.
a) Cross-section of the visible spectrum integrated photonic platform on 200-mm Si. The platform consists of two SiN waveguide layers (SiN1 and SiN2), a Si undercut, two metal layers (M1 and M2) connected by vias Via1 and Via2, titanium nitride (TiN) high resistivity heaters, P++, P, N, and N++ doped regions on a Si mesa for photodetection, and a deep trench for waveguide facets. The nominal dimensions are indicated. The cross-section of the PD, which has a PN (in a)) or PIN junction (intrinsic region width = 2 μm, a top view shown in d), is demarcated by the red dashed box. Wgap is the separation between the SiN1 layer and Si in the PD. b) A stitched scanning electron micrograph of the PD cross-section. A protective layer had been applied for the focused ion beam (FIB) milling to prepare the sample for imaging. Inset: Transmission electron micrograph showing the SiN waveguide above the Si. c) An optical micrograph of a PD with an input SiN waveguide. d) Top-view schematic of the PD test structure with a reference waveguide for power calibration. Pin,ref and Pout,ref are reference input and output optical powers; Wgw is the width of the routing waveguides; and Pin,PD is the input optical power into the PD.
Abstract of the Publication
Visible and near-infrared spectrum photonic integrated circuits are quickly becoming a key technology to address the scaling challenges in quantum information and biosensing. Thus far, integrated photonic platforms in this spectral range have lacked integrated photodetectors. Here, we report silicon nitride-on-silicon waveguide photodetectors that are monolithically integrated in a visible light photonic platform on silicon. Owing to a leaky-wave silicon nitride-on-silicon design, the devices achieved a high external quantum efficiency of >60% across a record wavelength span from λ ~ 400 nm to ~640 nm, an opto-electronic bandwidth up to 9 GHz, and an avalanche gain-bandwidth product up to 173 ± 30 GHz. As an example, a photodetector was integrated with a wavelength-tunable microring in a single chip for on-chip power monitoring.
