Stretchable Inorganic GaN-Nanowire Photosensor with High Photocurrent and Photoresponsivity

Abstract

To effectively implement wearable systems, their constituent components should be made stretchable. We successfully fabricated highly efficient stretchable photosensors made of inorganic GaN nanowires (NWs) as light-absorbing media and graphene as a carrier channel on polyurethane substrates using the pre-strain method. When a GaN-NW photosensor was stretched at a strain level of 50%, the photocurrent was measured to be 0.91 mA, corresponding to 87.5% of that (1.04 mA) obtained in the released state, and the photoresponsivity was calculated to be 11.38 A/W. These photosensors showed photocurrent and photoresponsivity levels much higher than those previously reported for any stretchable semiconductor-containing photosensor. To explain the superior performances of the stretchable GaN-NW photosensor, it was approximated as an equivalent circuit with resistances and capacitances, and in this way, we analyzed the behavior of the photogenerated carriers, particularly at the NW–graphene interface. In addition, the buckling phenomenon typically observed in organic-based stretchable devices fabricated using the pre-strain method was not observed in our photosensors. After a 1000-cycle stretching test with a strain level of 50%, the photocurrent and photoresponsivity of the GaN-NW photosensor were measured to be 0.96 mA and 11.96 A/W, respectively, comparable to those measured before the stretching test. To evaluate the potential of our stretchable devices in practical applications, the GaN-NW photosensors were attached to the proximal interphalangeal joint of the index finger and to the back of the wrist. Photocurrents of these photosensors were monitored during movements made about these joints.

Surface-dependent band structure variations and bond deviations of GaN

“…26 Electrical and photoconductivity properties of GaN nanowires have been studied. [27][28][29][30][31] Recently, an intrinsic {0001} GaN wafer cut to expose {10% 10} side faces has been used for facet-specific electrical conductivity and photoluminescence measurements, showing that the {0001} face is much more conductive than the {10% 10} face. 32 However, the {10% 10} face gives much stronger photoluminescence than the {0001} face does.…”

Flexible 1.3 μm photodetector fabricated with InN nanowires and graphene on overhead projector transparency sheet

“…According to the previous works on the flexible and stretchable photosensors fabricated with GaN NWs and graphene, the effect of uneven surfaces on the device performance could be neglected due to the conformal contact. 10,48 That is, the conformal contact, in which the top graphene layer wraps the surface of the InN NWs, minimizes unintentional scattering and recombination of photogenerated carriers at the interface between the NWs and graphene. Consequently, the photogenerated carriers in the InN NWs can migrate into the graphene channel without significant loss.…”

“…50 Because of the conformal contact and high electron mobility of the graphene channel, the alignment of the InN NWs also rarely affects the device performance. 10,48 That is, the generation rate of carriers by light absorption at the InN NWs dominantly influences the device performance.…”

“…9 For example, Han et al demonstrated flexible and stretchable photosensors operating from ultraviolet to visible wavelengths using GaN NWs and graphene. 9,10 In the same way, InN NWs can be used as active media for flexible photodetectors operating at the wavelength of 1.3 μm. The most commonly used approach for the formation of InN NWs is the vapor-liquid-solid process, in which external metal catalysts act as forming seeds to promote the anisotropic growth of NWs.…”

Drastic improvement in photoelectrochemical water splitting performance over prolonged reaction time using new carrier-guiding semiconductor nanostructures

“…1a shows a schematic diagram of the process used to grow the InGaN/GaN CSNWs with structures protruding from the surface of the Si(111) substrate using plasma-assisted molecular-beam epitaxy (MBE). As the rst step (Step 1) in the formation of the InGaN/GaN CSNWs, 109 nm long GaN NWs are formed using the so-called "Ga pre-deposition" method, [34][35][36][37][38] and these NWs are used as nucleation seeds. A eld-emission scanning electron microscopy (FE-SEM) image, an X-ray diffraction (XRD) rocking curve, a photoluminescence (PL) spectrum, and transmission electron microscopy (TEM) images of the GaN NWs are shown in Fig.…”