- The paper introduces BP mid-IR photodetectors achieving 82 A/W responsivity through high photoconductive gain and low dark current.
- The study utilizes exfoliated BP films on silicon substrates with quadruple and interdigitated electrodes to capture polarization-sensitive photocurrents.
- The findings suggest BP’s promise for next-generation industrial monitoring, biomedical sensing, and high-speed polarimetric imaging.
Black Phosphorus Mid-Infrared Photodetectors with High Gain
The paper presents an advancement in the field of photonics by introducing black phosphorus (BP) as an effective material for mid-infrared (mid-IR) photodetectors with high internal gain. BP, a layered material with a moderate bandgap and superior carrier mobility, has emerged as a potential candidate for various optoelectronic applications, distinguishing itself from traditional materials such as mercury cadmium telluride and indium arsenide due to its anisotropic electronic properties and flexible substrate integration.
Key Findings and Methodology
The authors describe the development of BP-based photodetectors that operate efficiently at the mid-IR wavelength of 3.39 μm. This material showcases an external responsivity of 82 A/W and the capability to detect light at the pico-watt (pW) range. The substantial responsivity is attributed to the high photoconductive gain and low dark current, a result of BP's moderate bandgap which suppresses dark current more effectively than gapless graphene.
A salient feature of BP is its unique polarization-dependent response, resulting from its low crystalline symmetry. BP's anisotropic properties enable detection schemes sensitive to light polarization, expanding application possibilities in imaging and sensing under low-light conditions. The devices leverage the intrinsic properties of BP's puckered structure, enabling high speed and low detection limits achievable even at kilohertz modulation frequencies.
Device Fabrication and Photocurrent Measurements
The research team fabricated the photodetectors by exfoliating BP thin films and deposited them on a silicon substrate, forming transistors with quadruple electrodes. Detailed measurements of photoresponse as a function of incident light polarization and photocurrent collection direction were performed using scanning photocurrent imaging. The devices were engineered to exploit BP's asymmetric band structure, enhancing photo-carrier collection efficiency and responsivity.
Two distinct photosensitive mechanisms were discovered: the photovoltaic effect and the photo-gating effect. The dominance of the photo-gating effect, especially at low incident power, was linked to the extended lifetime of photo-generated carriers and the modulation of threshold voltage dictated by trapped carriers acting as a local gate.
Further investigations at mid-IR wavelengths involved employing BP with interdigitated electrodes, yielding similar responsivity characteristics and confirming the efficacy of this configuration in mid-IR imaging applications. These measurements stressed the dynamic range and noise performance of the photodetectors.
Implications and Future Directions
The demonstrated BP photodetectors hold promise for next-generation mid-IR applications encompassing industrial monitoring, threat detection, and biomedical sensing. The findings underscore BP's advantage in integrating with silicon and flexible substrates, a critical attribute for developing scalable, chip-level devices.
The observed polarization sensitivity introduces potential innovations in polarimetry and imaging enhancing target contrast, especially in optically dense environments. Future research could explore optimizing BP-based detectors for specific applications in digital imaging and expand on the exploitation of BP's anisotropic attributes to refine detection schemes requiring polarization assessment.
The results provide compelling evidence supporting continued research into black phosphorus and its integration into existing and novel photodetector technologies, potentially influencing the design of photonic devices with enhanced spectral responses tailored for high-bandwidth, low-noise applications.