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Abstract
Due to the requirements of oceanography exploration and detection, self-powered photodetectors (PDs) with low-power consumption are essential for the next-generation optoelectronic applications. In this work, we successfully demonstrate a self-powered photoelectrochemical (PEC) PD in seawater based on the (In,Ga)N/GaN core-shell heterojunction nanowires. Compared to those of the PD in pure water, it is found that the upward and downward overshooting features of current can be the key reason contributing to the much faster response speed of the PD in seawater. Thanks to the enhanced response speed, the rise time of PD can be reduced more than 80%, and the fall time remains only 30% by applying in seawater instead of pure water. The key factors of generating these overshooting features should be the instantaneous temperature gradient, carrier accumulation and elimination on the semiconductor/electrolyte interfaces at the moments of light on and off. By the analysis of experimental results, the Na+ and Cl- ions are proposed to be the main factors affecting the PD behavior in seawater, which can enhance the conductivity and accelerate the oxidation-reduction reaction significantly. This work paves an effective way to develop the new self-powered PDs for the wide applications in under-seawater detection and communication.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Without an external power supply, self-powered photodetectors (PDs) can be the indispensable parts in the communication systems and photoelectric sensing technology [1–6]. Due to the advantages of low cost and self-powered supply [2,7,8], photoelectrochemical (PEC) PD can extend the applications of self-powered PDs in freshwater or even seawater [9–11]. Because of the potential advantage of high safety, underwater wireless optical communication (UWOC) is considered as an important alternative candidate for radio frequency (RF) communications and acoustic communications [12]. The seawater communication is significant for future applications in the activities of oceanography exploration and detection [12–14]. Hence, self-powered PEC PDs have the great potential to be applied in seawater communication and detection, such as the environmental monitoring and marine-resource exploration.
Seawater has a low attenuation of light waves in the wavelength range from 450 to 550 nm, which is regarded as blue-green light transmission window [13,15,16]. With the direct and adjustable energy band, the band gap of (In,Ga)N can cover the wavelength ranging from 365 nm to 1700 nm, while that of (Al,Ga)N covers the wavelength ranging from 200 nm to 365 nm [17,18]. Thus, compared with (Al,Ga)N, (In,Ga)N with appropriate In composition is more suitable to be used for under-seawater communication. Furthermore, compared with the films or bulk materials, nanowires (NWs) have the larger surface-to-volume ratio, which could increase the optical absorption and photogenerated carrier density [17,19]. In addition to the extraordinary characteristics of long lifetime, being nontoxic and high stability against radiation and electrochemical (EC) etching [20,21], (In,Ga)N NWs can be the excellent candidate for making PDs for under-seawater applications.
In our previous work, we fabricated the self-powered PEC PDs by GaN and (Al,Ga)N NWs successfully [18,22,23]. An underwater communication system was prepared to demonstrate that such PEC PDs can be used for underwater detection [18]. However, due to the existence of a large number of ions (e.g., Na+ and Cl-) and foreign substances in seawater [12,24], seawater is quite different from pure water. That means the performance of PEC PD in seawater is likely to be quite different from that in pure water. Moreover, for under-seawater detection, (In,Ga)N NWs are better than both (Al,Ga)N and GaN NWs because of blue-green light transmission window. Up to now, although it is very promising to develop such self-powered PD in seawater, very few works have been reported about utilizing (In,Ga)N NWs in under-seawater detection. Therefore, it is still quite necessary and attractive to fabricate (In,Ga)N NWs PDs for under-seawater detection.
In this work, the (In,Ga)N/GaN core-shell heterojunction NWs have been designed and utilized in fabricating a self-powered PEC PD in seawater. Both the (In,Ga)N NWs and PEC PD can be easily fabricated without complicated processes. Apart from the photocurrent and response time, the stability and underlying mechanism of the self-powered PEC PD have also been studied.
2. Experimental section
2.1 Preparation of GaN NWs
Molecular beam epitaxy (MBE, Vecco G20) was used to prepare the (In,Ga)N NWs on silicon (Si) substrates (Fig. 1(a)). In the growth chamber of MBE, the 2-inch n-type Si(111) substrate should be heated up to 900 °C for about 15 min to eliminate native oxides. The growth chamber contains the Ga effusion cell and N plasma cell. Initially, the substrate temperature was set to be 830 °C. A GaN segment was grown with a nominal Ga flux of ∼2.0 × 10−8 Torr for 2 h. After that, we grew (In,Ga)N segment with a nominal In flux of ∼8.5 × 10−9 Torr for about 1 h without doping. In this stage, the substrate temperature was decreased to 630 °C. Finally, a GaN segment was grown for about 0.5 h as a cap. During the epitaxial process, the nitrogen flow rate and plasma power were kept at 4.8 sccm and 450 W, respectively.
Fig. 1. (a) Prepare the (In,Ga)N NWs by MBE. (b) Connect the conducing wire to the Si substrate. (c) Measure the performance of the PD in the electrolytes. (d) Side-view and (e) top-view SEM images of (In,Ga)N NWs. (f) Side-view STEM image and high-resolution EDX mapping of the (In,Ga)N section in NWs. (g) The AC-STEM image and (h) the corresponding FFT of (In,Ga)N crystals within a NW.
2.2 Fabrication of self-powered PEC PDs
First, the as-grown (In,Ga)N NW samples were divided into small pieces. By a welding torch, the In/Au/Al alloys were melted on the back side of Si(111) to connect the conducting wire (Fig. 1(b)). To avoid the EC corrosion and leakage current, these In/Au/Al alloys were coated by epoxy resin. Except the MBE epitaxial, the cost for fabricating a PEC PD was estimated to be less than $\$$0.8, including the In/Au/Al alloys, epoxy resin and conducting wires.
2.3 Characterization and measurements
To characterize the optical properties, photoluminescence (PL, SP2500i, Princeton Instruments) system with a 405 nm laser was utilized. Scanning electron microscopy (SEM, S-4800, HITACHI) and spherical aberration-corrected scanning transmission electron microscopy (AC-STEM) with a high-resolution energy dispersive X-ray (EDX) mapping were utilized to characterize the NW morphology and element distribution. Focused ion beam (FIB, Scios, FEI) was utilized to prepare the STEM samples. An EC workstation with PEC system (DH 7000) was used to evaluate the electrical properties of PDs in a reaction vessel with the electrolytes of pure water NaCl solution and seawater. The self-powered PD characteristics were measured at zero-voltage bias by the lighting sources of light-emitting-diodes (LEDs) with different wavelengths (Fig. 1(c)). During the underwater measurements, the NW sample and Pt plate were used as the working and counter electrodes, respectively. The seawater was collected from seacoast of Hainan, China (Fig. S1, Supplement 1).
3. Results and discussion
As illustrated in Fig. 1(d), the NWs are well vertically aligned on the Si substrate. The height of the NWs is around 1 µm. According to Fig. 1(d)–1(f), the diameter of (In,Ga)N segment is larger than that of bottom GaN segment. The energy-dispersive X-ray (EDX) mapping image (Fig. 1(f)) and PL peaks (Fig. S2) confirm the existence of In element within NWs. Furthermore, a GaN cap is on the top of (In,Ga)N segment, which agrees well with the experimental design. From Fig. S2, the PL result has two peaks centered at around 565 nm and 694 nm. Different NW diameters can lead to different In components within (In,Ga)N sections, which could mainly contribute to the dual PL peaks [17]. According to physical properties with Vegard's law [25], the band gap of InxGa1-xN can be calculated as the following:
b is the bowing parameter of (In,Ga)N, which is selected as 1.43 eV [26]. The band gap of InN and GaN is 0.7 eV and 3.4 eV, respectively [17]. From Eq. (1), the In components of (In,Ga)N NWs corresponding to the peaks of ∼565 nm and ∼694 nm in Fig. S2 are ∼33% and ∼47%, respectively. As illustrated in Fig. 1(g), the fringe lattice of the GaN segment is around 2.7 Å, which could be assigned to the lattice spacing between two adjacent planes, indicating the growth direction along the c-axis [27]. Figure 1(h) shows the corresponding fast Fourier transform (FFT) image of Fig. 1(g). Such clear lattice fringe and FFT image is the testimony of a good crystallinity, indicating the a-plane wurtzite nitride binaries of GaN crystals [28–31].As illustrated in Figs. 2(a)–2(c), all the photocurrent results of the PDs in the pure water, NaCl solution and seawater exhibit the regular on-off behavior. The NaCl concentration in seawater was reported to be about 3.5% [24,32]. Thus, the characteristics of the PD in the solution with 3.5% NaCl concentration are studied here. The photocurrent (Iphoto) is calculated as the following [7]:
Ilight and Idark are the current with and without illumination, respectively. Compared with those in Fig. 2(a), both Ilight and Idark in Fig. 2(b) and 2(c) are much higher. Moreover, both the fall time (tf, defined as the time required for the photocurrent falls to 10% of Ifall) and rise time (tr, defined as the time required for photocurrent increases to 90% of the maximum value) are the key parameters of the PD response [33]. In this work, Ifall is defined as the follow:Fig. 2. Photo-switching behavior of the PDs in (a) the pure water, (b) the solution with 3.5% NaCl concentration, and (c) the seawater under 490 nm illumination. (d) Photocurrent of the PD in the solution with different NaCl concentrations.
As shown in Fig. 2(b), I0 is the current before light off, and Imin represents the minimum current. Compared to those of PD in pure water, both tr and tf of PD in NaCl solution and seawater are reduced significantly, leading the much faster response speed. Hence, the electrolyte is an important factor to affect the photocurrent and response speed of PEC PD. From Fig. 2(d), Ilight can be increased significantly when increasing the NaCl concentration in solution from 0 to 0.2%. However, with the further increase of NaCl concentration in solution, Ilight tends to be saturated.
From Fig. 3(a), both tr and tf decrease rapidly when increasing the NaCl concentration from 0 to 0.2%. Then, they become stable when the NaCl concentration is larger than 0.2%. In other words, when the NaCl concentration is larger than 0.2%, the effect of Na+ and Cl- ions accelerating the response speed becomes limited. As shown in Table 1, tr and tf of this PD in both NaCl solution and seawater are much higher than those comprising of GaN NWs in Ref. [22,34]. Therefore, the Na+ and Cl- ions have the reference significance for further improving the response speed of PEC PDs made of different materials. In general, GaN-based materials have excellent stability. With the PD continuously working from 0 to ∼9,000 s, the photocurrent shows a low fluctuation (< 6%, Fig. 3(b)), indicating the high stability of the PD.
Fig. 3. (a) Response time as a function of NaCl concentration. (b) Long-time photocurrent behavior of PD in seawater at 0 V bias.
Table 1. Comparison between this work and recently reported self-powered PEC PDs with nanostructures.
Compared with those of the PD in pure water, the Iphoto data of PD in both NaCl solution and seawater are much higher at different incident light-power densities (Fig. 4(a)). As the key parameters of PD, responsivity (R) and external quantum efficiency (ηEQE) are calculated as the follows [41]:
Pinc is the incident light-power density (490 nm, ∼8 mW/cm2) and SPD is the area of (In,Ga)N NWs (∼64 mm2). More details of calibrating Pinc can be found in Ref. [18]. h is Planck’s constant and ν is the frequency of incident light. q is the elementary charge. At different wavelengths, R and ηEQE of the PD in both NaCl solution and seawater are also much higher than those of the PD in pure water (Fig. 4(b) and 4(c)). In the range from 400 nm to 520 nm, R and ηEQE show an overall upward trend, which mainly depend on the absorption efficiency of (In,Ga)N and the transmissivity of seawater. In addition, all the photocurrent, R and ηEQE data of the PDs in NaCl solution and seawater are comparative, as well as the photo-switching characteristics in Fig. 2(b) and 2(c). In the device measurements (Fig. 1(c)), the PD was immersed in the electrolyte, which could absorb the emitting photons. However, such loss of photons is neglected to simplify the measurements. Furthermore, it is normal to use the monochromatic wavelength for calculating ηEQE [42], which is the peak wavelength of lighting source (LED). However, the wavelength of LED is not monochromatic, which has a non-negligible full-width at half-maximum (FWHM). That means the photons with the shorter or longer wavelengths than 490 nm could be harder to reach the semiconductor surface. According to Fig. 4(d), the operating bias voltage should be another key factor affecting ηEQE [42]. Therefore, the actual R and ηEQE are proposed to be larger than those shown in Fig. 4(b) and 4(c), especially for those of PDs operating at forward bias instead of 0 V bias.Fig. 4. (a) Current as a function of light-power density under 490 nm illumination. (b) Responsivity and (c) EQE of PDs at different wavelengths. (d) Current density as a function of potential. The inset shows the current densities of the PD measured in pure water.
At 1 V bias, the PD in the higher NaCl concentration can achieve the larger current density (Fig. S3). However, the current density tends to be saturated when the concentration of NaCl is in a high level. From Fig. 4(d), the current densities of the PD in all electrolytes increase with the bias voltage. Under illumination, the current densities of the PD in all electrolytes can also be increased, proving the generation of photocurrent. Furthermore, the current densities and response time (Fig. 3(a)) of the PD in both 3.5% NaCl solution and seawater are comparative. The concentration of NaCl in seawater was about 3.5%. As a result, it is proposed that the Na+ and Cl- ions are the main factors affecting the PD behavior in seawater.
To better study the underlying mechanism of the PEC PD in seawater, the schematic illustrations are plotted in Fig. 5. From Fig. 5(a), photogenerated holes transport to water, while the electrons transport to the conducting wire. The (In,Ga)N/GaN core-shell heterojunction could provide both vertical and horizontal directions for the carrier transports (Fig. 5(b)). When the GaN section contacts with the electrolyte of seawater, an EC equilibrium is established by conveying excess carriers through the top and side NW/electrolyte interfaces (Fig. 5(b)). The photoelectric current is likely to be produced via the following reactions [7,43–45]:
Fig. 5. (a) Schematic illustrations of the self-powered PEC PD in seawater under 490 nm illumination and (b) the enlarged (In,Ga)N/GaN core–shell heterojunction NW. The energy band diagrams of the PD in the stages of (c) light on, (d) continuously lighting, and (e) light off.
The whole circuit with both light harvest and carrier transport can be completed without the external bias, leading to the self-powered characteristics [11]. The segment of GaN cap was designed to protect the (In,Ga)N segment from EC corrosion. As the GaN shell on the sidewall of (In,Ga)N is very thin (< 7 nm, Fig. 1(f), 5(b)), the photogenerated carriers can pass through it easily by diffusion or tunneling (Fig. 5(c)) [21,46]. Furthermore, the area of (In,Ga)N sidewall is much larger than that of (In,Ga)N top surface (Fig. 1(f)). Therefore, it is proposed that the GaN cap only has a very limited effect on the carrier transport.
In Figs. 5(c)–5(e), the energy band values and electronic affinity come from Ref. [30,47–49]. Under illumination, carriers are excited to the conduction band (EC) and valence band (EV), producing electron-hole pairs. When the 490 nm light is turned on (Process I in Fig. 2(c)), the photocarriers can be immediately generated within the (In,Ga)N segment (Fig. 5(c)). Then the photogenerated holes can easily move towards the semiconductor/electrolyte interface [50], leading to the instantaneous accumulation of photogenerated carriers on the semiconductor/electrolyte surfaces [20]. The light-induced heating of the semiconductor/electrolyte interface could cause a sharp transient current spike, which consists of current generated by both pyroelectric and photoelectric effects in semiconductor/electrolyte heterojunction [51]. In the seawater, Na+ and Cl- can enhance the conductivity and accelerated the oxidation-reduction reaction significantly (Eq. (8)-(10)), leading to that the sharp positive current in seawater (Fig. 2(c)) is much higher than that in pure water (Fig. 2(a)). Then, the pyroelectric current disappears due to the absence of a temperature gradient, and a part of carriers will be quickly lost via the nonradiative transition (Fig. 5(d)), resulting in the rapid decrease (Process II in Fig. 2(c)). Compared with that in Fig. 2(a), such overshooting feature of photocurrent can be the key reason contributing to the decreased rise time (tr: 0.05 vs 0.29 s). After that, the current density recovers to a new steady state under continuous illumination. When the light is turned off, little photocarriers could be generated within the (In,Ga)N segment (Fig. 5(e)). Furthermore, due to the sudden decrease in temperature, an opposite pyroelectric response and a sharp reverse current can be generated (Process III in Fig. 2(c)) [51]. After that, thanks to the excellent conductivity with a lot of Na+ and Cl- ions, the current density recovers to a new steady state quickly (Process IV in Fig. 2(c)). Compared with that in Fig. 2(a), such downward overshooting feature of current can be the key reason contributing to the much smaller tf (0.03 vs 0.1 s).
4. Conclusion
In this work, a self-powered PEC PD in seawater based on the (In,Ga)N/GaN core-shell heterojunction NWs has been fabricated successfully and economically. The GaN shell can be used to protect the (In,Ga)N core from the EC corrosion. As it is very thin, GaN shell is proposed to have a very limited effect on the carrier transport due to the existence of carrier diffusion and tunneling. By analyzing the experimental results, the Na+ and Cl- ions are proposed to be the main factors affecting the PD performance in seawater by accelerating the oxidation-reduction reaction and enhancing the conductivity. When the light is turned on and off, the instantaneous temperature gradient, carrier accumulation and elimination on the semiconductor/electrolyte interfaces exist, which can be the key factors of generating the sharp transient current. Compared to those of the PD in pure water, such overshooting features of current can be the key reason contributing to reduce the response time of PD in seawater significantly (tr: 0.05 vs 0.29 s; tf: 0.03 vs 0.1 s). Therefore, the self-powered PDs based on vertical (In,Ga)N NWs have broad application prospects in the underwater photoelectric sensing technology, environmental monitoring and marine-resource exploration where requiring the low cost and low-power consumption.
Funding
Key Research Program of Frontier Science, Chinese Academy of Sciences (ZDBS-LY-JSC034); Jiangsu Key Disciplines of the Fourteenth Five-Year Plan (2021135); Research Program of Scientific Instrument and Equipment of CAS (YJKYYQ20200073); National Natural Science Foundation of China (62174172, 61827823, 61875224); Suzhou Institute of Nano-Tech and Nano-Bionics (SINANO) (Y8AAQ21001).
Acknowledgments
The authors are thankful for the technical support from Vacuum Interconnected Nanotech Workstation (Nano-X, No. F2201), Platform for Characterization & Test of SINANO, CAS.
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
Supplemental document
See Supplement 1 for supporting content.
References
1. X. Liu, H. Gao, J. E. Ward, X. Liu, B. Yin, T. Fu, J. Chen, D. R. Lovley, and J. Yao, “Power generation from ambient humidity using protein nanowires,” Nature 578(7796), 550–554 (2020). [CrossRef]
2. D. Wang, X. Liu, S. Fang, C. Huang, Y. Kang, H. B. Yu, Z. Liu, H. Zhang, R. Long, Y. Xiong, Y. Lin, Y. Yue, B. Ge, T. K. Ng, B. S. Ooi, Z. Mi, J.-H. He, and H. Sun, “Pt/AlGaN nanoarchitecture: toward high responsivity, self-powered ultraviolet-sensitive photodetection,” Nano Lett. 21(1), 120–129 (2021). [CrossRef]
3. H. Fang, C. Zheng, L. Wu, Y. Li, J. Cai, M. Hu, X. Fang, R. Ma, Q. Wang, and H. Wang, “Solution-processed self-powered transparent ultraviolet photodetectors with ultrafast response speed for high-performance communication system,” Adv. Funct. Mater. 29(20), 1809013 (2019). [CrossRef]
4. L.-H. Zeng, D. Wu, S.-H. Lin, C. Xie, H.-Y. Yuan, W. Lu, S. P. Lau, Y. Chai, L.-B. Luo, Z.-J. Li, and Y. H. Tsang, “Controlled synthesis of 2D palladium diselenide for sensitive photodetector applications,” Adv. Funct. Mater. 29(1), 1806878 (2019). [CrossRef]
5. D. Wu, J. Guo, J. Du, C. Xia, L. Zeng, Y. Tian, Z. Shi, Y. Tian, X. J. Li, Y. H. Tsang, and J. Jie, “Highly polarization-sensitive, broadband, self-powered photodetector based on graphene/PdSe2/germanium heterojunction,” ACS Nano 13(9), 9907–9917 (2019). [CrossRef]
6. L.-H. Zeng, S.-H. Lin, Z.-J. Li, Z.-X. Zhang, T.-F. Zhang, C. Xie, C.-H. Mak, Y. Chai, S. P. Lau, L.-B. Luo, and Y. H. Tsang, “Fast, self-driven, air-stable, and broadband photodetector based on vertically aligned PtSe2/GaAs heterojunction,” Adv. Funct. Mater. 28(16), 1705970 (2018). [CrossRef]
7. D. Wang, C. Huang, X. Liu, H. Zhang, H. Yu, S. Fang, B. S. Ooi, Z. Mi, J. H. He, and H. Sun, “Highly uniform, self-assembled AlGaN nanowires for self-powered solar-blind photodetector with fast-response speed and high responsivity,” Adv. Opt. Mater. 9, 2000893 (2020). [CrossRef]
8. H. Ma, L. Jia, Y. Lin, H. Fang, W. Wu, L. Wu, B. Hu, and H. Wang, “A self-powered photoelectrochemical ultraviolet photodetector based on Ti3C2Tx/TiO2 in situ formed heterojunctions,” Nanotechnology 33(7), 075502 (2022). [CrossRef]
9. H. Lin, L. Wei, C. Wu, Y. Chen, S. Yan, L. Mei, and J. Jiao, “High-performance self-powered photodetectors based on ZnO/ZnS core-shell nanorod arrays,” Nanoscale Res. Lett. 11(1), 420 (2016). [CrossRef]
10. Q. Li, L. Wei, Y. Xie, K. Zhang, L. Liu, D. Zhu, J. Jiao, Y. Chen, S. Yan, G. Liu, and L. Mei, “ZnO nanoneedle/H2O solid-liquid heterojunction-based self-powered ultraviolet detector,” Nanoscale Res. Lett. 8(1), 415 (2013). [CrossRef]
11. Y. Luo, D. Wang, Y. Kang, X. Liu, S. Fang, M. H. Memon, H. Yu, H. Zhang, D. Luo, X. Sun, B. S. Ooi, C. Gong, Z. Xu, and H. Sun, “Demonstration of Photoelectrochemical-Type Photodetectors Using Seawater as Electrolyte for Portable and Wireless Optical Communication,” Adv. Opt. Mater. 10(3), 2102839 (2022). [CrossRef]
12. H. Chen, X. Chen, J. Lu, X. Liu, J. Shi, L. Zheng, R. Liu, X. Zhou, and P. Tian, “Toward long-distance underwater wireless optical communication based on a high-sensitivity single photon avalanche diode,” IEEE Photonics J. 12(3), 7902510 (2020). [CrossRef]
13. R. Lin, X. Liu, G. Zhou, Z. Qian, X. Cui, and P. Tian, “InGaN micro-LED array enabled advanced underwater wireless optical communication and underwater charging,” Adv. Opt. Mater. 9(12), 2002211 (2021). [CrossRef]
14. Z. Lv, G. He, C. Qiu, Y. Fan, H. Wang, and Z. Liu, “CMOS monolithic photodetector with a built-in 2-dimensional light direction sensor for laser diode based underwater wireless optical communications,” Opt. Express 29(11), 16197–16204 (2021). [CrossRef]
15. D. Yu, F. Cao, Y. Gu, Z. Han, J. Liu, B. Huang, X. Xu, and H. Zeng, “Broadband and sensitive two-dimensional halide perovskite photodetector for full-spectrum underwater optical communication,” Nano Res. 14(4), 1210–1217 (2021). [CrossRef]
16. X. Sun, C. Kang, M. Kong, O. Alkhazragi, Y. Guo, M. Ouhssain, Y. Weng, B. H. Jones, T. K. Ng, and B. S. Ooi, “A review on practical considerations and solutions in underwater wireless optical communication,” J. Lightwave Technol. 38(2), 421–431 (2020). [CrossRef]
17. J. Zhang, M. Zhou, D. Wu, L. Bian, Y. Zhao, H. Qin, W. Yang, Y. Wu, Z. Xing, and S. Lu, “Dual-wavelength visible photodetector based on vertical (In,Ga)N nanowires grown by molecular beam epitaxy,” RSC Adv. 11(26), 15632–15638 (2021). [CrossRef]
18. M. Jiang, Y. Zhao, L. Bian, W. Yang, J. Zhang, Y. Wu, M. Zhou, S. Lu, and H. Qin, “Self-powered photoelectrochemical (Al,Ga)N photodetector with an ultrahigh ultraviolet/visible reject ratio and a quasi-invisible functionality for 360° omnidirectional detection,” ACS Photonics 8(11), 3282–3290 (2021). [CrossRef]
19. J. Jeong, Q. Wang, J. Cha, D. K. Jin, D. H. Shin, S. Kwon, B. K. Kang, J. H. Jang, W. S. Yang, Y. S. Choi, J. Yoo, J. K. Kim, C.-H. Lee, S. W. Lee, A. Zakhidov, S. Hong, M. J. Kim, and Y. J. Hong, “Remote heteroepitaxy of GaN microrod heterostructures for deformable light-emitting diodes and wafer recycle,” Sci. Adv. 6(23), eaaz5180 (2020). [CrossRef]
20. Z. Xing, Y. Zhao, L. Bian, J. Zhang, M. Zhou, W. Yang, Y. Wu, M. Jiang, J. Long, and S. Lu, “Economically detaching transparent and flexible (Al,Ga)N nanowire films with improved photoelectric response in view of ultraviolet photodetectors,” Mater. Adv. 2(3), 1006–1015 (2021). [CrossRef]
21. M. Zhou, H. Qiu, T. He, J. Zhang, W. Yang, S. Lu, L. Bian, and Y. Zhao, “UV photodetector based on vertical (Al, Ga)N nanowires with graphene electrode and Si substrate,” Phys. Status Solidi A 217(15), 2000061 (2020). [CrossRef]
22. J. Zhang, B. Jiao, J. Dai, D. Wu, Z. Wu, L. Bian, Y. Zhao, W. Yang, M. Jiang, and S. Lu, “Enhance the responsivity and response speed of self-powered ultraviolet photodetector by GaN/CsPbBr3 core-shell nanowire heterojunction and hydrogel,” Nano Energy 100, 107437 (2022). [CrossRef]
23. M. Jiang, J. Zhang, W. Yang, D. Wu, Y. Zhao, Y. Wu, M. Zhou, and S. Lu, “Flexible self-powered photoelectrochemical photodetector with ultrahigh detectivity, ultraviolet/visible reject ratio, stability, and a quasi-invisible functionality based on lift-off vertical (Al,Ga)N nanowires,” Adv. Mater. Interfaces 9(16), 2200028 (2022). [CrossRef]
24. X. Guan, F. A. Chowdhury, N. Pant, L. Guo, L. Vayssieres, and Z. Mi, “Efficient unassisted overall photocatalytic seawater splitting on GaN-based nanowire arrays,” J. Phys. Chem. C 122(25), 13797–13802 (2018). [CrossRef]
25. A. R. Denton and N. W. Ashcroft, “Vegard's law,” Phys. Rev. A 43(6), 3161–3164 (1991). [CrossRef]
26. J. Wu, W. Walukiewicz, K. M. Yu, J. W. Ager, E. E. Haller, H. Lu, and W. J. Schaff, “Small band gap bowing in In1-xGaxN alloys,” Appl. Phys. Lett. 80(25), 4741–4743 (2002). [CrossRef]
27. D. Wang, X. Liu, Y. Kang, X. Wang, Y. Wu, S. Fang, H. Yu, M. H. Memon, H. Zhang, W. Hu, Z. Mi, L. Fu, H. Sun, and S. Long, “Bidirectional photocurrent in p–n heterojunction nanowires,” Nat. Electron. 4(9), 645–652 (2021). [CrossRef]
28. Z. Wang, R. Fu, F. Li, H. Xie, P. He, Q. Sha, Z. Tang, N. Wang, and H. Zhong, “One-step polymeric melt encapsulation method to prepare CsPbBr3 perovskite quantum dots/polymethyl methacrylate composite with high performance,” Adv. Funct. Mater. 31(22), 2010009 (2021). [CrossRef]
29. J. Song, J. Li, L. Xu, J. Li, F. Zhang, B. Han, Q. Shan, and H. Zeng, “Room-temperature triple-ligand surface engineering synergistically boosts ink stability, recombination dynamics, and charge injection toward EQE-11.6% perovskite QLEDs,” Adv. Mater. 30(30), 1800764 (2018). [CrossRef]
30. I. Vurgaftman and J. R. Meyer, “Band parameters for nitrogen-containing semiconductors,” J. Appl. Phys. 94(6), 3675–3696 (2003). [CrossRef]
31. Y. Zhou and G. H. Wu, Analysis Methods in Materials Science: X-ray Diffraction and Electron Microscopy in Materials Science (Harbin Institute of Technology, 1998), pp. 265–296.
32. G. Liu, “Oxygen evolution reaction electrocatalysts for seawater splitting: a review,” J. Electroanal. Chem. 923, 116805 (2022). [CrossRef]
33. M. Jiang, J. Zhang, Z. Xing, D. Wu, H. Qin, L. Bian, Y. Zhao, W. Yang, and S. Lu, “Self-powered visible photodetector with fast-response speed and high stability based on vertical (In,Ga)N nanowires,” OSA Continuum 4(9), 2381–2390 (2021). [CrossRef]
34. M. Zhang, Y. Liu, M. Yang, W. Zhang, J. Zhou, Z. Zhang, E. Xie, X. Pan, and S. Li, “High performance self-powered ultraviolet photodetectors based on electrospun gallium nitride nanowires,” Appl. Surf. Sci. 452, 43–48 (2018). [CrossRef]
35. C. He, D. Guo, K. Chen, S. Wang, J. Shen, N. Zhao, A. Liu, Y. Zheng, P. Li, Z. Wu, C. Li, F. Wu, and W. Tang, “α-Ga2O3 nanorod array–Cu2O microsphere p–n junctions for self-powered spectrum-distinguishable photodetectors,” ACS Appl. Nano Mater. 2(7), 4095–4103 (2019). [CrossRef]
36. D. Ma, R. Wang, J. Zhao, Q. Chen, L. Wu, D. Li, L. Su, X. Jiang, Z. Luo, Y. Ge, J. Li, Y. Zhang, and H. Zhang, “A self-powered photodetector based on two-dimensional boron nanosheets,” Nanoscale 12(9), 5313–5323 (2020). [CrossRef]
37. N. Liu, H. Qiao, K. Xu, Y. Xi, L. Ren, N. Cheng, D. Cui, X. Qi, X. Xu, W. Hao, S. X. Dou, and Y. Du, “Hydrogen terminated germanene for a robust self-powered flexible photoelectrochemical photodetector,” Small 16(23), 2000283 (2020). [CrossRef]
38. B. Wang, Y. Zhou, Z. Huang, H. Qiao, C. Duan, X. Ren, Z. Wang, J. Zhong, and X. Qi, “Photoelectrochemical self-powered photodetector based on 2D liquid-exfoliated bismuth nanosheets: with novel structures for portability and flexibility,” Mater. Today Nano 14, 100109 (2021). [CrossRef]
39. H. Qiao, Z. Li, Z. Huang, X. Ren, J. Kang, M. Qiu, Y. Liu, X. Qi, J. Zhong, and H. Zhang, “Self-powered photodetectors based on 0D/2D mixed dimensional heterojunction with black phosphorus quantum dots as hole accepters,” Appl. Mater. Today 20, 100765 (2020). [CrossRef]
40. D. Li, G. Xing, S. Tang, X. Li, L. Fan, and Y. Li, “Ultrathin ZnSe nanowires: one-pot synthesis via a heat-triggered precursor slow releasing route, controllable Mn doping and application in UV and near-visible light detection,” Nanoscale 9(39), 15044–15055 (2017). [CrossRef]
41. C. Lu, M. Luo, W. Dong, Y. Ge, T. Han, Y. Liu, X. Xue, N. Ma, Y. Huang, Y. Zhou, and X. Xu, “Bi2Te3/Bi2Se3/Bi2S3 cascade heterostructure for fast-response and high-photoresponsivity photodetector and high-efficiency water splitting with a small bias voltage,” Adv. Sci., 2205460 (2022). [CrossRef]
42. S. Dhar, T. Majumder, and S. P. Mondal, “Graphene quantum dot-sensitized ZnO nanorod/polymer schottky junction uv detector with superior external quantum efficiency, detectivity, and responsivity,” ACS Appl. Mater. Interfaces 8(46), 31822–31831 (2016). [CrossRef]
43. A. G. Wallace and M. D. Symes, “Decoupling strategies in electrochemical water splitting and beyond,” Joule 2(8), 1390–1395 (2018). [CrossRef]
44. K. Zhang, M. Ma, P. Li, D. H. Wang, and J. H. Park, “Water splitting progress in tandem devices: moving photolysis beyond electrolysis,” Adv. Energy Mater. 6(15), 1600602 (2016). [CrossRef]
45. J. Zhang, S. Cao, W. Hu, and L. Piao, “Hydrogen production by photoelectrocatalytic seawater splitting,” Progress in Chemistry 32, 1376–1385 (2020). [CrossRef]
46. D. You, C. Xu, J. Zhao, F. Qin, W. Zhang, R. Wang, Z. Shi, and Q. Cui, “Single-crystal ZnO/AlN core/shell nanowires for ultraviolet emission and dual-color ultraviolet photodetection,” Adv. Opt. Mater. 7(6), 1801522 (2019). [CrossRef]
47. S. N. Mohammad and H. Morkoc, “Progress and prospects of group-III nitride semiconductors,” Prog. Quantum Electron. 20(5-6), 361–525 (1996). [CrossRef]
48. E. Liu, The Physics of Semiconductors, 7th ed. (Publishing House of Electronic Industry, 2011), pp. 385–388.
49. J. Sun, S. Zhang, T. Zhan, Z. Liu, J. Wang, X. Yi, J. Li, P. M. Sarro, and G. Zhang, “A high responsivity and controllable recovery ultraviolet detector based on a WO3 gate AlGaN/GaN heterostructure with an integrated micro-heater,” J. Mater. Chem. C 8(16), 5409–5416 (2020). [CrossRef]
50. X. Liu, D. Wang, Y. Kang, S. Fang, H. Yu, H. Zhang, M. H. Memon, J. H. He, B. S. Ooi, H. Sun, and S. Long, “Photovoltage-competing dynamics in photoelectrochemical devices: achieving self-powered spectrally distinctive photodetection,” Adv. Funct. Mater. 32(5), 2104515 (2022). [CrossRef]
51. R. Ahmadi, A. Abnavi, H. Ghanbari, H. Mohandes, M. R. Mohammadzadeh, T. De Silva, A. Hasani, M. Fawzy, F. Kabir, and M. M. Adachi, “Self-powered, broadband, and polarization-sensitive pyroelectric-photoelectric photodetector based on silicon-water heterojunction,” Nano Energy 98, 107285 (2022). [CrossRef]
