Chalcogenide glass waveguide-integrated black phosphorus mid-infrared photodetectors

Abstract

Black phosphorus (BP) is a promising 2D material that has unique in-plane anisotropy and a 0.3 eV direct bandgap, making it an attractive material for mid-IR photodetectors. So far, waveguide integrated BP photodetectors have been limited to the near-IR on top of Si waveguides that are unable to account for BP's crystalline orientation. In this work, we employ mid-IR transparent chalcogenide glass (ChG) both as a broadband mid-IR transparent waveguiding material to enable waveguide-integration of BP detectors, and as a passivation layer to prevent BP degradation during device processing as well as in ambient atmosphere post-fabrication. Our ChGon-BP approach not only leads to the first demonstration of mid-IR waveguide-integrated BP detectors, but also allows us to fabricate devices along different crystalline axes of BP to investigate, for the first time, the impact of in-plane anisotropy on photoresponse of waveguideintegrated devices. The best device exhibits responsivity up to 40 mA W −1 and noise equivalent power as low as 30 pW Hz −1/2 at 2185 nm wavelength. We also found that photodetector responsivities changed by an order of magnitude with different BP orientations. This work validates BP as an effective photodetector material in the mid-IR, and demonstrates the power of the glass-on-2D-material platform for prototyping of 2D material photonic devices.

Synthesis Techniques, Optoelectronic Properties, and Broadband Photodetection of Thin‐Film Black Phosphorus

“…[ 3,4,6,217,218 ] Thin‐film BP, as a novel vdW layered material, offers another opportunity for broadband photodetection applications due to its widely tunable bandgap, anisotropic optical properties and high compatibility with silicon platforms. In this section, we systematically review the development of BP‐based MIR photodetectors, which can be summarized in three aspects: (1) Intrinsic BP photodetectors with cutoff wavelength of 4 µm; [ 48,101,219–224 ] (2) BP photodetectors with cutoff wavelength beyond 4 µm, enabled by the electric field [ 100 ] or alloying; [ 96,98,103,225 ] (3) MIR photodetectors based on vdW heterojunctions. [ 15,103,226 ] It should be noted that MIR is generally referred to light with wavelength ranging from 2.5 to 25 µm, in some reports people also define it as 2–20 µm wavelength regime.…”

“…[ 15,103,226 ] It should be noted that MIR is generally referred to light with wavelength ranging from 2.5 to 25 µm, in some reports people also define it as 2–20 µm wavelength regime. [ 222,223 ] Since BP‐based photodetectors operating in visible and near‐infrared region have been extensively explored [ 59–61,102,227–236 ] and summarized by several good review works, [ 237–239 ] we will not spare more texts to introduce them again. To characterize the performance of a photodetector, some terminologies should be introduced, such as photocurrent ( I ph ), responsivity ( R ), 3 dB bandwidth (BW), noise equivalent power (NEP), detectivity ( D* ), external quantum efficiency (EQE), and response speed.…”

“…Hence, coupling with waveguide provides an effective strategy to enhance photon absorption of BP film and performance of detectors. [ 221–223 ]…”

“…[ 222 ] Chalcogenide glass (ChG)‐BP coupled detector is also demonstrated with transparent ChG serving as protection shell as well as waveguide material (Figure 11c). [ 223 ] The fabrication process, during which ChG is firstly evaporated onto BP film, followed by lithograph technique to fabricate waveguide structure, enables the rapid prototyping of BP photodetectors with various sample thickness and crystalline orientation. [ 223 ] The photodetector exhibits a maximized photoresponsivity of 40 mA W −1 and a low noise equivalent power of 30 pW Hz −1/2 at 2185 nm incident light.…”

“…[ 223 ] The fabrication process, during which ChG is firstly evaporated onto BP film, followed by lithograph technique to fabricate waveguide structure, enables the rapid prototyping of BP photodetectors with various sample thickness and crystalline orientation. [ 223 ] The photodetector exhibits a maximized photoresponsivity of 40 mA W −1 and a low noise equivalent power of 30 pW Hz −1/2 at 2185 nm incident light. In addition to the utilization of SOI [ 221,222 ] and ChG [ 223 ] waveguide system, the adoption of optical cavity is also expected to further enhance the optical absorption of BP.…”