High-Performance Free-Standing Flexible Photodetectors Based on Sulfur-Hyperdoped Ultrathin Silicon

Quintic refractive index profile-based funnel-shaped silicon antireflective structures for enhanced photodetector performance

Antireflection, vital in optoelectronics devices such as solar cells and photodetectors, reduces light reflection and increases absorption. Antireflective structures (ARS), a primary method by which to realize this effect, control the refractive index (RI) profile based on their shape. The antireflection efficiency depends on the refractive index profile, with the quintic RI profile being recognized as ideal for superior antireflection. However, fabricating nano-sized structures with a desired shape, particularly in silicon with a quintic RI profile, has been a challenge. In this study, we introduce a funnel-shaped silicon (Si) ARS with a quintic RI profile. Its antireflective properties are demonstrated through reflectance measurements and by an application to a photodetector surface. Compared to the film Si and cone-shaped ARS types, which are common structures to achieve antireflection, the funnel-shaped ARS showed reflectance of 4.24% at 760 nm, whereas those of the film Si and cone-shaped ARS were 32.8% and 10.6%, respectively. Photodetectors with the funnel-shaped ARS showed responsivity of 0.077 A/W at 950 nm, which is 19.54 times higher than that with the film Si and 2.45 times higher than that with the cone-shaped ARS.

Transfer-printing-enabled GeSn flexible resonant-cavity-enhanced photodetectors with strain-amplified mid-infrared optical responses

Mid-infrared (MIR) flexible photodetectors (FPDs) constitute an essential element for wearable applications, including health-care monitoring and biomedical detection. Compared with organic materials, inorganic semiconductors are promising candidates for FPDs owing to their superior performance as well as optoelectronic properties. Herein, for the first time, we present the use of transfer-printing techniques to enable a cost-effective, nontoxic GeSn MIR resonant-cavity-enhanced FPDs (RCE-FPDs) with strain-amplified optical responses. A narrow bandgap nontoxic GeSn nanomembrane was employed as the active layer, which was grown on a silicon-on-insulator substrate and then transfer-printed onto a polyethylene terephthalate (PET) substrate, eliminating the unwanted defects and residual compressive strain, to yield the MIR RCE-FPDs. In addition, a vertical cavity was created for the GeSn active layer to enhance the optical responsivity. Under bending conditions, significant tensile strain up to 0.274% was introduced into the GeSn active layer to effectively modulate the band structure, extend the photodetection in the MIR region, and substantially enhance the optical responsivity to 0.292 A W^-1 at λ = 1770 nm, corresponding to an enhancement of 323% compared with the device under flat conditions. Moreover, theoretical simulations were performed to confirm the strain effect on the device performance. The results demonstrated high-performance, nontoxic MIR RCE-FPDs for applications in flexible photodetection.

Screen-Printable Silver Paste Material for Semitransparent and Flexible Metal-Semiconductor-Metal Photodetectors with Liquid-Phase Procedure

Photodetectors are widely applied in modern industrial fields because they convert light energy into electrical signals. We propose a printable silver (Ag) paste electrode for a highly flexible metal–semiconductor–metal (MSM) broadband visible light photodetector as a wearable and portable device. Single-crystal and surface-textured silicon substrates with thicknesses of 37.21 μm were fabricated using a wet etching process. Surface texturization on flexible Si substrates enhances the light-trapping effect and minimizes reflectance from the incident light, and the average reflectance is reduced by 16.3% with pyramid-like structures. In this study, semitransparent, conductive Ag paste electrodes were manufactured using a screen-printing with liquid-phase process to form a flexible MSM broadband visible light photodetector. The transmittance of the homemade Ag paste solution fell between 34.83% and 36.98% in the wavelength range of visible light, from 400 nm to 800 nm. The highest visible light photosensitivity was 1.75 × 10⁴ at 19.5 W/m². The photocurrents of the flexible MSM broadband visible light photodetector were slightly changed under concave and convex conditions, displaying stable and durable bending properties.

High performance visible-SWIR flexible photodetector based on large-area InGaAs/InP PIN structure

Mechanically flexible optoelectronic devices and systems can enable a much broader range of applications than what their rigid counterparts can do, especially for novel bio-integrated optoelectronic systems, flexible consumer electronics and wearable sensors. Inorganic semiconductor could be a good candidate for the flexible PD when it can keep its high performance under the bending condition. Here, we demonstrate a III–V material-based flexible photodetector operating wavelength from 640 to 1700 nm with the high detectivity of 5.18 × 10¹¹ cm‧Hz^1/2/W and fast response speed @1550 nm by using a simply top-to-down fabrication process. The optoelectrical performances are stable as the PDs are exposed to bending cycles with a radius of 15 mm up to 1000 times. Furthermore, the mechanical failure mode of the PD is also investigated, which suggests that the cracking and delamination failure mode are dominant in bending up and bending down direction, respectively. Such a flexible III–V material-based PD and design with stable and high performance could be a promising strategy for the application of the flexible broad spectrum detection.

Room-temperature fabrication of SiC microwire photodetectors on rigid and flexible substrates via femtosecond laser direct writing

Flexible ultraviolet (UV) photodetectors (PDs) have gained increasing demand because of their widespread applications in wearable devices. However, difficulties associated with complicated fabrication technologies significantly limit their scope of application. Herein, via the development of a femtosecond laser direct writing (FsLDW) strategy, silicon carbide (SiC) nanoparticles are found to be assembled in a single microwire within 30 s. The surface of the deposited SiC microwire presents a three-dimensional porous structure, which is conducive to improving the responsivity of the device. The responsivity of a SiC-based microwire PD to UV light at 365 nm is found to be 55.89 A W-1 at a 1 V bias. The as-fabricated SiC microwire PDs on a glass substrate exhibit thermal stability at 350 °C, and the response speed of the PDs becomes notably faster at high temperatures, suggesting their promising applications in harsh conditions. Due to the low-temperature processing characteristics of this process, they can be prepared not only on glass substrates, but also on thermosensitive polymer substrates without an extra transfer process. Moreover, the SiC microwires prepared via FsLDW are directly deposited on the flexible substrate, and the prepared flexible SiC-based PDs can still work stably after being bent 2000 times. This research unveils a feasible way to fabricate a PD with excellent thermal stability and mechanical flexibility.