High-Speed, Self-Biased Broadband Photodetector-Based on a Solution-Processed Ag Nanowire/Si Schottky Junction

Picoampere Dark Current and Electro-Opto-Coupled Sub-to-Super-linear Response from Mott-Transition Enabled Infrared Photodetector for Near-Sensor Vision Processing

Light-intensity selective superlinear photodetectors with ultralow dark current can provide an essential breakthrough for the development of high-performing near-sensor vision processing. However, the development of near-sensor vision processing is not only conceptually important for device operation (given that sensors naturally exhibit linear/sublinear responses), but also essential to get rid of the massive amount of data generated during object sensing and classification with noisy inputs. Therefore, achieving the giant superlinear photoresponse while maintaining the picoampere leakage current, irrespective of the measurement bias, is one of the most challenging tasks. Here, Mott material (vanadium dioxide) and silicon-based integrated infrared photodetectors are developed that show giant superlinear photoresponse (exponent >18) and ultralow dark current of 4.46 pA. Specifically, the device demonstrates an electro-opto-coupled insulator-to-metal transition, which leads to outstanding photocurrent on/off ratio (>10⁶ ), a high responsivity (>1 mA W^-1 ), and excellent detectivity (>10¹²  Jones), while maintaining response speed (τ_r  = 6 µs and τ_f  = 10 µs). Further, intensity-selective near-sensor processing is demonstrated and night vision pattern reorganization even with noisy inputs is exhibited. This research will pave the way for the creation of high-performance photodetectors with potential uses, such as in night vision, pattern recognition, and neuromorphic processing.

Facilely Achieved Self-Biased Black Silicon Heterojunction Photodiode with Broadband Quantum Efficiency Approaching 100

Photodiodes are fundamental components in modern optoelectronics. Heterojunction photodiodes, simply configured by two different contact materials, have been a hot research topic for many years. Currently reported self-biased heterojunction photodiodes routinely have external quantum efficiency (EQE) significantly below 100% due to optical and electrical losses. Herein, an approach that virtually overcomes this 100% EQE challenge via low-aspect-ratio nanostructures and drift-dominated photocarrier transport in a heterojunction photodiode is proposed. Broadband near-ideal EQE is achieved in nanocrystal indium tin oxide/black silicon (nc-ITO/b-Si) Schottky photodiodes. The b-Si comprises nanostalagmites which balance the antireflection effect and surface morphology. The built-in electric field is explored to match the optical generation profile, realizing enhanced photocarrier transport over a broadband of photogeneration. The devices exhibit unprecedented EQE among the reported leading-edge heterojunction photodiodes: average EQE surpasses ≈98% for wavelengths of 570-925 nm, while overall EQE is greater than ≈95% from 500 to 960 nm. Further, only elementary fabrication techniques are explored to achieve these excellent device properties. A heart rate sensor driven by nanowatt faint light is demonstrated, indicating the enormous potential of this near-ideal b-Si photodiode for low power consuming applications.

Controllable, Self-Powered, and High-Performance Short-Wavelength Infrared Photodetector Driven by Coupled Flexoelectricity and Strain Effect

Mechanical deformation-induced strain gradients and coupled spontaneous electric polarization field in centrosymmetric materials, known as the flexoelectric effect, can generate ubiquitous mechanoelectrical functionalities, like the flexo-photovoltaic effect. Concurrently, nano/micrometer-scale inhomogeneous strain reengineers the electronic arrangements and in turn, could alter the fundamental limits of optoelectronic performance. Here, the flexoelectric effect-driven self-powered giant short-wavelength infrared (λ ≤ 1800 nm) photoresponse from centrosymmetric bulk silicon, indeed far beyond the fundamental bandgap (λ = 1100 nm) is demonstrated. Particularly, large on/off ratio (≈10⁵ ), extremely high sensitivity (2.5 × 10⁸ %), good responsivity of 96 mA W^-1 , decent specific detectivity of ≈1.54 × 10¹⁴ Jones, and a rapid response speed of ≈100 µs, even at nanoscale (<30 nm), are measured at λ = 1620 nm. The infrared response sensitivity is tuned in a wide range (up to 1.4 × 10⁸ %) by controlling the applied pointed force from 1 to 10 µN. These results confirm that emerging mechanoelectrical coupling not only sheds to achieve tunable optoelectronic performance beyond the fundamental limit, but also offers innovative numerous applications like mechanoptical switch, photovoltaic, sensors, and self-driving vehicles.

High-Performance and Self-Powered Alternating Current Ultraviolet Photodetector for Digital Communication

Self-powered ultraviolet photodetectors offer great potential in the field of optical communication, smart security, space exploration, and others; however, achieving high sensitivity with maintaining fast response speed has remained a daunting challenge. Here, we develop a titanium dioxide-based self-powered ultraviolet photodetector with high detectivity (≈1.8 × 10¹⁰ jones) and a good photoresponsivity of 0.32 mA W^-1 under pulsed illumination (λ = 365 nm, 4 mW cm^-2), which demonstrate an enhancement of 114 and 2017%, respectively, due to the alternating current photovoltaic effect compared to the conventional direct current photovoltaic effect. Further, the photodetector demonstrated a high on/off ratio (≈10³), an ultrafast rise/decay time of 112/63 μs, and a noise equivalent power of 5.01 × 10^-11 W/Hz^1/2 under self-biased conditions. Photoconductive atomic force microscopy revealed the nanoscale charge transport and offered the possibility to scale down the device size to a sub-10-nanometer (∼35 nm). Moreover, as one of the practical applications, the device was successfully utilized to interpret the digital codes. The presented results enlighten a new path to design energy-efficient ultrafast photodetectors not only for the application of optical communication but also for other advanced optoelectronic applications such as digital display, sensing, and others.

A mixed-dimensional 1D Se-2D InSe van der Waals heterojunction for high responsivity self-powered photodetectors

Mixed-dimension van der Waals (vdW) p-n heterojunction photodiodes have inspired worldwide efforts to combine the excellent properties of 2D materials and traditional semiconductors without consideration of lattice mismatch. However, owing to the scarcity of intrinsic p-type semiconductors and insufficient optical absorption of the few layer 2D materials, a high performance photovoltaic device based on a vdW heterojunction is still lacking. Here, a novel mixed-dimension vdW heterojunction consisting of 1D p-type Se nanotubes and a 2D flexible n-type InSe nanosheet is proposed by a facile method, and the device shows excellent photovoltaic characteristics. Due to the superior properties of the hybrid p-n junction, the mix-dimensional van der Waals heterojunction exhibited high on/off ratios (103) at a relatively weak light intensity of 3 mW cm-2. And a broadband self-powered photodetector ranging from the UV to visible region is achieved. The highest responsivity of the device could reach up to 110 mA W-1 without an external energy supply. This value is comparable to that of the pristine Se device at 5 V and InSe device at 0.1 V, respectively. Furthermore, the response speed is enhanced by one order of magnitude over the single Se or InSe device even at a bias voltage. This work paves a new way for the further development of high performance, low cost, and energy-efficient photodetectors by using mixed-dimensional vdW heterostructures.

Piezo-phototronic effect-modulated carrier transport behavior in different regions of a Si/CdS heterojunction photodetector under a Vis-NIR waveband

The piezo-phototronic effect, as a three-way coupling effect of piezoelectricity, semiconductor and optical excitation in piezoelectric semiconductors to improve the performance of optoelectronic devices, has a wide range of applications in various fields. However, under different light illumination conditions, the piezo-phototronic effect would have different effects on the optoelectronic performance due to the different photo-generated carrier excitation regions. Here, the piezo-phototronic effect is utilized to modulate the carrier transport behavior of a p-Si/n-CdS heterojunction PD during the optoelectronic process in a broadband range from visible to near-infrared light. The strain-induced piezo-charges significantly improve the photoresponse performance of the heterojunction PD. The photoresponsivity increases by 1867% under -0.35‰ strain under 808 nm light illumination, with a remarkable reduction in the rise and fall times to ∼2.1 ms (reduced by 83.3% and 50.0%, respectively). However, since the photo-generated carriers are produced only at the n-CdS side under 442 nm light illumination, the photoresponse performance is greatly weakened by the piezo-phototronic effect. The corresponding working mechanism of the piezo-phototronic effect on the heterojunction photodiode under different light illumination conditions is proposed in detail. These results provide an in-depth understanding about the piezo-phototronic effect, which would enable more efficient utilization of the piezo-phototronic effect in optoelectronic devices.

Structural Engineering of Si/TiO2/P3HT Heterojunction Photodetectors for a Tunable Response Range

To meet the demands of next-generation optoelectronic circuits, the design and construction of photodetectors with a tunable photoresponse range and self-powered feature are urgently required. To achieve selective wavelength detection, a band-pass filter is usually required to dislodge the interference of a certain wavelength light, which inevitably enhances the weight and increases the cost. Here, we demonstrate a self-powered photodetector with a tunable response range by constructing a heterojunction structure consisting of poly(3-hexylthiophene) (P3HT), a TiO₂ interlayer, and silicon nanowires. By controlling the P3HT concentration, both core-shell and embedded configurations can be obtained, which exhibit different response ranges. This work provides a convenient route to construct self-powered wavelength-selective photodetectors, which may find applications in light communication and biomedical engineering.