Fast Response Characteristics of Flexible Ultraviolet Photosensors with GaN Nanowires and Graphene

Abstract

We report the fast response characteristics of flexible ultraviolet photosensors with GaN nanowires (NWs) and a graphene channel. The GaN NWs used as light-absorbing media are horizontally and randomly embedded in a graphene sandwich structure in which the number of bottom graphene layers is varied from zero to three and the top is a fixed single layer of graphene. In the response curve of the photosensor with a double-layer bottom graphene, as obtained under pulsed illumination with a pulse width of 50 ms and a duty cycle of 50%, the rise and decay times were measured as 24.1 ± 0.1 and 28.2 ± 0.1 ms, respectively. The eye-crossing percentage was evaluated as 52.1%, indicating no substantial distortion of the duty cycle and no pulse symmetry problem. The rise and decay times estimated from an equivalent circuit analysis represented by resistances and capacitances agree well with the measured values. When the device was under the bending condition, the rise and decay times of the photosensor were comparable to those in the unbent state.

Facilitated Interfacial Electronic Processes by the π–π Stacked Edge-on Tetrabenzoporphyrin/Graphene Layer Enables Broadband Ultrasensitive Photodetecting with Prompt Response

“…Furthermore, the detecting efficiency at the NIR range is rather distinguished as well, as implied by the excellent data of R (290–570 A W –1 ) and D * (0.5–0.96) × 10 12 Jones). The achieved R and D * at the UV and NIR range stand out remarkably from those of previous reports, and their values for the visible lights are among the top levels of the former studies as well, as can be seen from the top ,,,− and bottom parts ,,− of Figures f or S2d (detailed photodetecting materials in the cited references provided).…”

Stretchable Inorganic GaN-Nanowire Photosensor with High Photocurrent and Photoresponsivity

“…The rise times (decay times) at the light intensity of 10, 20, 40, 60, and 80 mW/cm 2 were calculated to be 75.28 (135.25), 75.30 (135.33), 75.63 (135.53), 75.88 (135.71), and 75.99 ms (136.03 ms), respectively. The rise and decay times were defined as the time required for the current transition from 10 to 90% and from 90 to 10% of the steady-state photocurrent, respectively . The rise and decay times were slightly increased with increasing the light intensity because of the effect of thermal energy caused by incident light …”

“…30 Han et al reported highly efficient flexible photosensors with GaN NWs as light-absorbing media. 32,33 However, no stretchable photosensor using the III-nitride material system has been reported, largely due to its intrinsically brittle and rigid characteristics.…”

“…Since III-nitride semiconductor NWs are considered as effective light-absorbing media due to their high carrier mobility and wide band gaps covering from UV to NIR wavelengths, they are being actively studied for the applications in photosensors. − Various device structures have been proposed for flexible III-nitride-NW photosensors. − For example, Zhang et al demonstrated flexible photosensors using vertically aligned InGaN/GaN NWs fabricated on a flexible Cu substrate . Han et al reported highly efficient flexible photosensors with GaN NWs as light-absorbing media. , However, no stretchable photosensor using the III-nitride material system has been reported, largely due to its intrinsically brittle and rigid characteristics.…”

Detaching (In,Ga)N Nanowire Films for Devices Requiring High Flexibility and Transmittance

“…Flexible optoelectronic devices provide many novel functionalities and have the potential to open up a new branch of industry. − As another novel application, transparent devices have attracted considerable interest as next-generation display technology in various fields, including wearable intelligent electronics, automobile windshield navigation, and IoT (Internet of Things) applications. − Because of the extraordinary characteristics of low power consumption, being nontoxic, long lifetime, and high efficiency, GaN-based optoelectronic devices, e.g., light-emitting devices (LEDs), are promising for the above fields. , In addition, this material is also attractive for piezoelectric devices, such as piezoelectric sensors and piezoelectric transistors. − Thus, achieving flexible and transparent GaN-based films is a decisive step for future markets and applications. Over the past few years, the fabrication of flexible devices based on thin-film and micropyramid GaN-based materials has been intensively studied by developing procedures to transfer the epitaxial structures from the original rigid substrates used for growth to soft substrates. , These additional procedures usually require laser lift-off or selective wet etching of a thick sacrificial layer or the entire source substrate. ,− However, besides expensive laser equipment, the laser lift-off technology requires the bandgap of substrate should be larger than that of GaN, which limits its applications. , Furthermore, the sacrificial layers are normally thick, e.g., 2.5 μm in ref , or may need to be highly doped, which can increase the epitaxial cost and deteriorate the epitaxial quality.…”