Open Access
Add to BibSonomy
Abstract
Enhancement in the light interaction between plasmonic nanoparticles (NPs) and semiconductors is a promising way to enhance the performance of optoelectronic devices beyond the conventional limit. In this work, we demonstrated improved performance of Ga2O3 solar-blind photodetectors (PDs) by the decoration of Rh metal nanoparticles (NPs). Integrated with Rh NPs on oxidized Ga2O3 surface, the resultant device exhibits a reduced dark current of about 10 pA, an obvious enhancement in peak responsivity of 2.76 A/W at around 255 nm, relatively fast response and recovery decay times of 1.76 ms/0.80 ms and thus a high detectivity of ∼1013 Jones. Simultaneously, the photoresponsivity above 290 nm wavelength decreases significantly with improved rejection ratio between ultraviolet A (UVA) and ultraviolet B (UVB) regions, indicative of enhanced wavelength detecting selectivity. The plasmonic resonance features observed in transmittance spectra are consistent with the finite difference time-domain (FDTD) calculations. This agreement indicates that the enhanced electric field strength induced by the localized surface plasmon resonance is responsible for the enhanced absorption and photoresponsivity. The formed localized Schottky barrier at the interface of Rh/Ga2O3 will deplete the carriers at the Ga2O3 surface and lead to the remarkable reduced dark current and thus improve the detectivity. These findings provide direct evidence for Rh plasmonic enhancement in solar-blind spectral region, offering an alternative pathway for the rational design of high-performance solar-blind PDs.
© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
Solar-blind deep ultraviolet photodetectors (DUV PDs) of which response only in < 280 nm of incident light are attracting considerable interests owing to their versatile applications, including short-range communications, missile launching and tracking detection, ozone layer monitoring, space and astronomical research, security [1–16]. So far, many wide bandgap semiconductors such as AlGaN, MgZnO ternary materials and diamond have been used to fabricate solar-blind DUV PDs [17–26]. However, these materials require precisely controlled alloying engineering and the possible phase segregation would introduce various defects, which limit the device performance of solar-blind PDs. Owing to the intrinsic solar-blindness with a desirable bandgap of ∼4.9 eV, β-Ga2O3 has been demonstrated as a promising material for solar-blind DUV PDs without bandgap engineering. Moreover, the excellent chemical, mechanical and thermal stabilities make it an attractive substitute for the application of solar-blind PDs. At present, great progresses have been made in solar-blind DUV photodetectors based on Ga2O3 in various forms of bulk single crystals, epitaxial thin films, nanostructures, polycrystalline films or even amorphous layers [27–34]. For instance, K. Arora et al. demonstrated a polycrystalline β-Ga2O3 thin film PD fabricated on a cost-effective Si substrate. The photodetector yields a responsivity of 96.13 A/W with an external quantum efficiency of 4.76×104% at 5 V under the illumination of 250 nm monochromatic light. This developed photodetector also shows strong capability for the detection of weak incident signals at DUV region (44 nW/cm2) [35]. L. X. Qian et al. reported that the PDs fabricated from radiofrequency magnetron sputtered amorphous gallium oxide films exhibit high responsivity (70.26 A/W) and a large specific detectivity (1.26 × 1014 Jones) [36]. Therefore, the quality of Ga2O3 films is not the bottleneck of high-performance PDs. Alongside the epitaxy or deposition methods, it was reported that polycrystalline Ga2O3 films could be fabricated from a simple process, i.e. high-temperature oxidization from GaN thin films, which are mature on the industry [37]. W. T. Weng et al. reported that solar-blind Ga2O3 PDs fabricated by the furnace oxidized Ga2O3 thin film exhibit a responsivity of 0.453 A/W. However, such low responsivity is far from the performance of currently available commercial detectors, especially for the detection of extremely weak signals.
In the past two decades, surface plasmon polaritons (SPPs) or localized surface plasmons (LSPs) have drawn great attention as their ability to enhance the performance of the optoelectronic devices, e.g. light emitting diodes, solar cells, lasers and PDs [38–43]. Particularly, for UV PDs, X. Wang et al. proposed and demonstrated Ag nanoparticles (NPs)-decorated ZnO photodetectors for UV light sensing [44]. After the decoration of ZnO surface with randomly distributed Ag NPs, the dark current density of ZnO UV photodetectors decreases significantly. Additionally, the device exhibits an obvious increase in responsivity. D. B. Li et al. also reported that the high-responsivity GaN UV detectors have been realized by integrating Ag nanoparticles onto the surface of the devices [45]. The responsivity of these detectors can be enhanced by approximately 30 times by the localized surface plasmon effect. However, for the commonly used plasmonic metals such as Ag and Au, the SP coupling wavelength is in the near-UV and visible regions [44–46]. For solar-blind regions, S. J. Cui et al. demonstrated the solar-blind UV PDs based on Ga/Ga2O3 nanocomposite films with enhanced photoresponse, but the long response time is not desirable [47]. In some previous reports, it has been demonstrated that the SP coupling wavelength of Al is located in the DUV region. However, the easy oxidization of Al makes it difficult for practical application [48]. Therefore, searching for an alternative plasmonic metal integrated with conventional DUV devices is a strategy to improve the performance of the devices.
In this work, metal Rh NPs are implemented for the LSP coupling to enhance the performance of the oxidized Ga2O3 DUV PDs. After the decoration of the surface by the Rh NPs, the device shows an obvious spectral responsivity enhancement at the spectral region shorter than 290 nm. At approximately 255 nm, the peak responsivity of the Rh NPs decorated PDs is enhanced by approximately 2.76 times, from 1 A/W to 2.76 A/W. At the wavelength region above 290 nm, the spectral responsivity of the PDs is suppressed by the Rh NPs decoration, demonstrating an improved UVC/UVA rejection ratio and enhanced wavelength selectivity capability. Simultaneously, the device decorated by the Rh NPs exhibit a lower dark current of 10 pA, faster response and recovery times, and an enhanced detectivity up to 1.64 × 1013 Jones. The detailed physical mechanism for this phenomenon is attributed to the plasmonic scattering effect of these Rh NPs and the localized Schottky barrier at the interface of Rh/Ga2O3 which depletes the carriers at the surface of the Ga2O3.
2. Experiments
The Ga2O3 films were oxidized from n-type GaN films grown on c-plane sapphire wafers. The thickness, carrier concentration and the mobility of the GaN epi-layers were approximately 5 µm, 1.5×1016 cm−3, and 1.2×103 cm2/Vs, respectively. Prior to the oxidization process, the GaN/sapphire wafers were ultrasonic cleaned in acetone and isopropyl alcohol for 10 min, respectively. Then the GaN/sapphire wafers were dipped into a diluted hydrochloric acid water solution (HCl: H2O = 1:1) for 5 min to remove native oxide. Following that, the GaN/sapphire wafers were placed into a quartz tube furnace. The heating-up time from room temperature to 1000°C was around 55 min in the oxygen ambient. The oxidation of GaN was performed at 1000 °C for 60 min at atmospheric pressure. Finally, the samples were taken out from the oxidizing furnace when the temperature went down to 200 °C in the nitrogen environment. The oxidized Ga2O3 layers were measured to be approximately 500 nm by cross-sectional scanning electron microscopy (not shown here). After the oxidization process, 5 nm-thick Rh ultrathin films were deposited onto the Ga2O3 films by the electron beam evaporation at a pressure of 4${\times} $10−7 Torr. Then the samples were annealed by rapid thermal annealing (RTA 300) at 900 °C for 120 seconds in an N2 atmosphere to form Rh NPs. Subsequently, the interdigitated metal contacts (20 nm Cr/40 nm Au) were fabricated by means of standard photolithography (Karl-Suss MA6/BA6), DC magnetron sputtering and lift-off processes. Each device comprises of 10 pairs of interdigitated electrodes whose length, width, and spacing were 300 µm, 6 µm, and 6 µm, respectively. As a result, the effective illumination area was approximately 3.42×10−4 cm2. The fabricated photodetectors were finally annealed by rapid thermal annealing under the N2 atmosphere at 200 °C for 120 s. The preparation process of the control sample was identical except for the decoration of the Rh NPs. To verify the plasmon resonance features of Rh NPs, Rh NPs were fabricated on the sapphire substrate by the same method as mentioned above.
To characterize the properties of the materials, the surface morphology and microstructure were determined by a high-resolution field emission scanning electron microscope (FE-SEM, ZEISS SIGMA). The current-voltage (I–V) characteristics were measured using a Keithley 2410 SourceMeter and a Keithley 6514 programmable electrometer. A 450 W Xe arc lamp, a mechanical chopper, and a lock-in amplifier were used to measure the photocurrent response spectra. The system was calibrated with a standard Si detector. The devices were all illuminated perpendicularly from the front metal/semiconductor contact side. A 266 nm pulsed laser with a single pulse energy of 2 µJ was employed as the excitation source for transient photoresponse measurements, and a digital oscilloscope (Tektronix, TBS1102) was used for data collection with a loading resistance of 50 Ω. All measurements were carried out at room temperature.
3. Results and discussions
Figure 1(a) shows the SEM image of the surface morphology of the oxidized Ga2O3 films (denoted as sample A). Clearly, the oxidized Ga2O3 films are polycrystalline. The top surface is relatively rough with large grains of several hundred nanometers in size. Figure 1(b) shows the SEM image of the surface morphology of a Ga2O3 film decorated with Rh NPs (denoted as sample B). It indicates that the NP density is approximately 6.8×109 cm−2 and the statistical summary results in Fig. 1(c) shows that the radius distribution of NPs is mainly concentrated in the range of 20-40 nm.
Fig. 1. (a) Top-view FESEM image of Ga2O3 film without Rh NPs, (b) Top-view FESEM image of Ga2O3 film with Rh NPs, (c) Size distribution of Rh NPs.
A series of MSM DUV PDs were fabricated based on the prepared Ga2O3 films with and without Rh NPs. To explore the effect of Rh NPs on the performance of Ga2O3 PDs, the spectral photoresponse was measured from 240 to 400 nm at a fixed bias of 5 V. In general, the responsivity (R) of the photodetector is determined by the relation
where ${I_{Ph}}$ and ${I_{Dark}}$ are current measured under illumination and in dark condition, respectively, and ${p_\lambda }$ is the incident power density with a specific wavelength of λ. As illustrated in Fig. 2, both spectra show peaks at approximately 255 nm and the peak responsivities for samples A and B are approximately 1.01 A/W and 2.76 A/W, respectively. The responsivity of sample B is higher than that of sample A at the wavelength region shorter than approximately 300 nm. The responsivity enhancement should be attributed to the plasmonic effect of the Rh NPs. To investigate the resonance wavelength of the fabricated Rh NPs, the finite difference time-domain (FDTD) simulations have been carried out. The simulated extinction spectra of the isolated Rh nanosphere with different radius are shown in Fig. 3(a). The resonance peak of Rh NP plasmons shows an obvious shift to the low energy side with the increasing particle radius. When the radius is in the range of 20-40 nm, that is, the range of the size distribution of the Rh NPs we fabricated, the plasmon resonance peak is located in the spectral region of 220-280 nm. This result indicates that the fabricated Rh NPs’ plasmonic energy matches the energy band of Ga2O3 quite well, which facilitates plasma-induced resonant energy transfer and promotes the excitation of electrons in Ga2O3, thus leading to the enhanced absorption cross-section and improved photoresponse from 240 to 300 nm. The transmittance spectrum of the Rh NPs fabricated on the sapphire substrate by the same method mentioned above is shown in Fig. 3(b). A dip centered at approximately 250 nm is shown in the transmittance spectrum. It is quite consistent with FDTD calculations and further illustrates the enhanced photoresponsivity in the DUV region is a result of the plasmonic effect induced by decorated Rh NPs.Fig. 2. Comparison of photoresponsivity vs wavelengths at 5V bias of the sample A and sample B. The inset shows the spectral response from 280 to 400 nm.
Fig. 3. The FDTD simulated extinction spectra of Rh NP with different radius and the experimental transmission spectrum of the Rh NPs on sapphire.
However, for the wavelength ranging from 300 to 400 nm, one can see from the inset in Fig. 2 that the responsivity of sample B is lower than that of sample A. At approximately 360 nm (the wavelength corresponding to the bandgap of GaN), sample B exhibits a responsivity of 3.14 mA/W compared to the 9.69 mA/W for sample A. It suggests that Rh NPs decorated Ga2O3 PDs can not only enhance the responsivity of the PDs in the UVC region, but also suppress the responsivity in the UVA region, thus leading to an improved UVC-to-UVA rejection ratio. This suppression phenomenon in the near UV region cannot be interpreted in the framework of the plasmonic resonance effect and thus additional physical mechanism should be taken into account. In general, there are three possible mechanisms to enhance the responsivity of PDs by the plasmonic effect: (1) light scattering enhancement, (2) localized field enhancement and (3) thermal electron emission enhancement [45]. As well known, the light scattering is a far-field mechanism, while the localized field enhancement is a near-field feature, and both of their actions are taken within dozens of nm scale. The thermal electron emission requires direct contact between semiconductor and metal NPs. In this case, the localized field enhancement and thermal electron emission do not occur on GaN due to the existence of Ga2O3 film (∼ 500 nm) between Rh NPs and GaN film. Therefore, when the incident wavelength is above 300 nm, the shading effect of Rh NPs results in a decrease in the light absorption of Ga2O3/GaN heterojunction and thus reduces the responsivity of the PD in the near UV region.
Figure 4(a) shows the I-V characteristics of Ga2O3 PD recorded under the dark condition and under the illumination of 254 nm light. Obviously, the dark current of sample B is about 10 pA, which is about one order of magnitude lower than that of sample A, indicating that the Rh NPs can suppress the dark current of the PDs besides the photoresponse enhancement. It is attributed to the formation of localized Schottky junction between Ga2O3 and Rh NPs, which thus depletes the carriers near the surface of Ga2O3 and thus reduce the conductance of the entire Ga2O3 film. Figure 4(b) shows the schematic energy band diagram of Rh/Ga2O3. The difference between the work function of Rh NPs (∼4.98 eV) and the electron affinity of Ga2O3 (∼4.0 eV) inevitably introduces a localized Schottky barrier at the interface of Rh/Ga2O3. Thus, the presence of Rh NPs will introduce a localized depletion area on the Ga2O3 surface near the Rh NPs. [44]. Most importantly, the depletion region coincides with the local optical field induced by the Rh NPs, which can not only enhance the absorption of light, but also effectively accelerate the separation of photo-induced carriers. As a result, under 254 nm light illumination, the photocurrent of sample B is obviously higher than sample A. With a higher photocurrent and a lower dark current, the photo-to-dark ratio of sample B is over 106, much higher than that of sample A, demonstrating an excellent switching ability. Detectivity (D*) is another key figure-of-merit for PDs, which usually describes the smallest detectable signal. The detectivity (D*) could be expressed as
Fig. 4. (a) I-V characteristics of sample A and sample B in the dark and under 254 nm DUV illumination. (b) Schematic energy band diagrams of Ga2O3 with Rh nanoparticles.
where S (3.42×10−4 cm2) is the effective area under illumination, with the shot noise from IDark regarded as the major component in the total noise. The detectivity D* for sample B at 255 nm is calculated as 1.64 × 1013 Jones which is much larger than that of sample A (1.33 × 1012 Jones). One may notice that there are shifts of nearly 1.8V between the dark currents and photocurrents shown the I-V curve. This phenomenon was also shown in some previous reports [49–51]. We believe that this phenomenon can be attributed to the charge trapping effect. When the voltage sweeps from negative to positive bias in the dark condition, considering the structural disorders and oxygen vacancies as observed in the Ga2O3, electrons can be trapped in the defect levels of Ga2O3. A built-in electric field is formed in the Ga2O3 layer then. Thus the I-V curve deviates from the coordinate origin. When illuminated by the DUV light, electrons trapped by the defect levels can be re-excited into the conduction band. The built-in electric field disappears and the I-V curve should be symmetric to the coordinate origin.
To characterize the response speed of photodetectors, a 266 nm pulsed laser with a single pulse energy of 2 µJ was employed as the excitation source for transient photoresponse measurements. As shown in Figs. 5(a) and 5(b), the dynamic response of the two photodetectors presents good stability and reproducibility. The rise time (tr, defined as the time during which the current increases from 10% to 90% of the peak value) was approximately 3.18 and 1.76 ms for samples A and B, respectively. The decay time (td, defined as the time during which the current decays from 90% to 10% of the peak value) was 3.66 and 0.80 ms for samples A and B, respectively. Detailed analysis of the response decay features has been performed as followed. Photocurrent decays for sample B is well described by a single exponential decay function, while the transient decay features for sample A is nonexponential, which has to be fitted by a biexponential relaxation equation of
where I0 is the steady-state photocurrent, t is the time, A and B are the constants, and τ1 and τ2 are the relaxation time constants corresponding to two components (fast and slow), respectively. Usually, the fast component of the relaxation time is related to the band-to-band transition while the slow component is attributed to the transition involved with the traps [32]. The rise time constants (τr) and the decay time constants (τd) of sample B were 0.82 ms and 0.38 ms, respectively, which is faster than 0.53 ms/1.58 ms and 0.52 ms/1.97 ms of sample A. The distinct difference is that the slow decay tail can be observed in sample A but only the fast-response process is dominant in sample B. Indeed, the oxidized Ga2O3 films are non-stoichiometric with a large number of structural disorders and point defects such as oxygen vacancies, as confirmed by SEM and XPS measurements (not shown here). Therefore, the carrier trapping and de-trapping processes involved in these traps lead to the obvious slow decay tail observed for sample A. When Rh NPs decorate on the Ga2O3 surface, we propose that free electrons are injected into traps in Ga2O3 from the Rh NPs as long as the energy level of the defects is lower than the work function of Rh. For example, the donor levels of oxygen vacancies in Ga2O3 are 2.77, 3.10, and 3.40 eV with respect to valence band maximum (VBM), as shown in Fig. 4(b), all of which are lower than the work function of metal Rh (4.98 eV) [35]. The transfer time is as short as an order of fs [52], which could be estimated from the Pauli exclusion principle(i.e. ${\tau _t} = h/\Delta E$), where h is the Plank constant and ΔE is the energy difference between the work function of Rh and the energy level of the defects. As a result, when the light is switched into on or off states, the defect states filled with electrons do not participate in the carriers trapping/releasing process. In other words, the slow-response processes associated with traps are greatly suppressed in sample B, thus improved device response time. As shown in Fig. 5(c), the typical response speed of sample B shows deterioration after six months. This may be attributed to the absorption of H2O or other molecules because the devices are preserved in the atmospheric environment unpackaged. However, the response speed is still in the millisecond range with good reproducibility, indicating good stability of the devices.Fig. 5. Normalized temporal pulse response excited by 266 nm excimer pulse laser of sample A (a), sample B (b) and sample B preserved in the atmospheric environment for 6 months (c).
4. Conclusions
In this work, the solar-blind photodetectors based on Rh NPs decorated Ga2O3 films have been investigated. After the decoration of their surface with random Rh NPs, these devices exhibit an obvious increase in peak responsivity at around 255 nm, the responsivity of these detectors is increased from 1.01 A/W to 2.76 A/W. The response time is reduced from 3.18 ms/3.66 ms to 1.76 ms/0.80 ms. Moreover, the responsivity longer than 290 nm is suppressed significantly, improving the wavelength selectivity of the Rh decorated PDs. Both PDs exhibit excellent extremely low dark current (∼10−11 A), high detectivity (∼1013 Jones). The detailed mechanism for this phenomenon can be attributed to the plasmonic effect of these Rh NPs and the localized Schottky barrier at the interface of Rh/Ga2O3. Our findings reveal an additional effective and feasible pathways for the development of high-performance solar-blind PDs.
Funding
National Key Research and Development Program (2016YFB0400903); National Natural Science Foundation of China (61604124, 61874090, 61774081, 91850112); State Key R and D project of Jiangsu (BE2018115); Fundamental Research Funds for the Central Universities (20720170098).
Acknowledgments
All authors participated in the conception of the project, took part in the experiment and discussed the results. RFT wrote the first draft of the manuscript. KH, JDY, JYK and RZ revised the final manuscript. All authors have given approval to the final version of the manuscript.
Disclosures
The authors declare no conflicts of interest
References
1. H. Chen, K. Liu, L. Hu, A. A. Al-Ghamdi, and X. Fang, “New concept ultraviolet photodetectors,” Mater. Today 18(9), 493–502 (2015). [CrossRef]
2. Y. Zhao, J. Zhang, D. Jiang, C. Shan, Z. Zhang, B. Yao, D. Zhao, and D. Shen, “Ultraviolet photodetector based on a MgZnO film grown by radio-frequency magnetron sputtering,” ACS Appl. Mater. Interfaces 1(11), 2428–2430 (2009). [CrossRef]
3. L. Li, E. Auer, M. Liao, X. Fang, T. Zhai, U. K. Gautam, A. Lugstein, Y. Koide, Y. Bando, and D. Golberg, “Deep-ultraviolet solar-blind photoconductivity of individual gallium oxide nanobelts,” Nanoscale 3(3), 1120–1126 (2011). [CrossRef]
4. Y. C. Chen, Y. J. Lu, C. N. Lin, Y. Z. Tian, C. J. Gao, L. Dong, and C. X. Shan, “Self-powered diamond/β-Ga2O3 photodetectors for solar-blind imaging,” J. Mater. Chem. C 6(21), 5727–5732 (2018). [CrossRef]
5. D. Y. Guo, H. Z. Shi, Y. P. Qian, M. Lv, P. G. Li, Y. L. Su, Q. Liu, K. Chen, S. L. Wang, C. Cui, C. R. Li, and W. H. Tang, “Fabrication of β-Ga2O3/ZnO heterojunction for solar-blind deep ultraviolet photodetection,” Semicond. Sci. Technol. 32(3), 03LT01 (2017). [CrossRef]
6. J. W. Chu, F. M. Wang, L. Yin, L. Lei, C. Y. Yan, F. Wang, Y. Wen, Z. X. Wang, C. Jiang, L. P. Feng, J. Xiong, Y. R. Li, and J. He, “High-performance ultraviolet photodetector based on a few-Layered 2D NiPS3 Nanosheet,” Adv. Funct. Mater. 27(32), 1701342 (2017). [CrossRef]
7. D. Y. Guo, Z. P. Wu, Y. H. An, X. C. Guo, X. L. Chu, C. L. Sun, L. H. Li, P. G. Li, and W. H. Tang, “Oxygen vacancy tuned Ohmic-Schottky conversion for enhanced performance in β-Ga2O3 solar-blind ultraviolet photodetectors,” Appl. Phys. Lett. 105(2), 023507 (2014). [CrossRef]
8. R. Lin, W. Zheng, D. Zhang, Z. Zhang, Q. Liao, L. Yang, and F. Huang, “High-performance graphene/β- Ga2O3 heterojunction deep-ultraviolet photodetector with hot-electron excited carrier multiplication,” ACS Appl. Mater. Interfaces 10(26), 22419–22426 (2018). [CrossRef]
9. S. Cui, Z. Mei, Y. Zhang, H. Liang, and X. Du, “Room-temperature fabricated amorphous Ga2O3 high-response-speed solar-blind photodetector on rigid and flexible substrates,” Adv. Opt. Mater. 5(19), 1700454 (2017). [CrossRef]
10. Y. Li, T. Tokizono, M. Liao, M. Zhong, Y. Koide, I. Yamada, and J.-J. Delaunay, “Efficient assembly of bridged β-Ga2O3 nanowires for solar-blind photodetection,” Adv. Funct. Mater. 20(22), 3972–3978 (2010). [CrossRef]
11. D. Y. Guo, Z. P. Wu, P. G. Li, Y. H. An, H. Liu, X. C. Guo, H. Yan, G. F. Wang, C. L. Sun, L. H. Li, and W. H. Tang, “Fabrication of β-Ga2O3 thin films and solar-blind photodetectors by laser MBE technology,” Opt. Mater. Express 4(5), 1067–1076 (2014). [CrossRef]
12. W. Zheng, R. Lin, J. Ran, Z. Zhang, X. Ji, and F. Huang, “Vacuum-ultraviolet photovoltaic detector,” ACS Nano 12(1), 425–431 (2018). [CrossRef]
13. W. Zheng, R. Lin, Y. Zhu, Z. Zhang, X. Ji, and F. Huang, “Vacuum ultraviolet photodetection in two-dimensional oxides,” ACS Appl. Mater. Interfaces 10(24), 20696–20702 (2018). [CrossRef]
14. J. J. Luo, S. R. Li, H. D. Wu, Y. Zhou, Y. Li, J. Liu, J. H. Li, K. H. Li, F. Yi, G. D. Niu, and J. Tang, “Cs2AgInCl6 double perovskite single crystals: parity forbidden transitions and their application for sensitive and fast UV photodetectors,” ACS Photonics 5(2), 398–405 (2018). [CrossRef]
15. L. Sang, M. Liao, and M. Sumiya, “A comprehensive review of semiconductor ultraviolet photodetectors: from thin film to one-dimensional nanostructures,” Sensors 13(8), 10482–10518 (2013). [CrossRef]
16. M. Razeghi, “Short-wavelength solar-blind detectors-status, prospects, and markets,” Proc. IEEE 90(6), 1006–1014 (2002). [CrossRef]
17. Z. G. Shao, D. J. Chen, H. Lu, R. Zhang, D. P. Cao, W. J. Luo, Y. D. Zheng, L. Li, and Z. H. Li, “High-gain AlGaN solar-blind avalanche photodiodes,” IEEE Electron Device Lett. 35(3), 372–374 (2014). [CrossRef]
18. T. Tut, M. Gokkavas, A. Inal, and E. Ozbay, “AlxGa1-xN-based avalanche photodiodes with high reproducible avalanche gain,” Appl. Phys. Lett. 90(16), 163506 (2007). [CrossRef]
19. Z. Huang, J. Li, W. Zhang, and H. Jiang, “AlGaN solar-blind avalanche photodiodes with enhanced multiplication gain using back-illuminated structure,” Appl. Phys. Express 6(5), 054101 (2013). [CrossRef]
20. Y. Huang, D. J. Chen, H. Lu, K. X. Dong, R. Zhang, Y. D. Zheng, L. Li, and Z. H. Li, “Back-illuminated separate absorption and multiplication AlGaN solar-blind avalanche photodiodes,” Appl. Phys. Lett. 101(25), 253516 (2012). [CrossRef]
21. T. Tut, M. Gokkavas, B. Butun, S. Butun, E. Ulker, and E. Ozbay, “Experimental evaluation of impact ionization coefficients in AlxGa1-xN based avalanche photodiodes,” Appl. Phys. Lett. 89(18), 183524 (2006). [CrossRef]
22. J. Yu, C. X. Shan, J. S. Liu, X. W. Zhang, B. H. Li, and D. Z. Shen, “MgZnO avalanche photodetectors realized in Schottky structures,” Phys. Status Solidi RRL 7(6), 425–428 (2013). [CrossRef]
23. X. H. Xie, Z. Z. Zhang, C. X. Shan, H. Y. Chen, and D. Z. Shen, “Dual-color ultraviolet photodetector based on mixed-phase-MgZnO/i-MgO/p-Si double heterojunction,” Appl. Phys. Lett. 101(8), 081104 (2012). [CrossRef]
24. J. Yu, C. X. Shan, X. M. Huang, X. W. Zhang, S. P. Wang, and D. Z. Shen, “ZnO-based ultraviolet avalanche photodetectors,” J. Phys. D: Appl. Phys. 46(30), 305105 (2013). [CrossRef]
25. A. Balducci, M. Marinelli, E. Milani, M. E. Morgada, A. Tucciarone, G. Verona-Rinati, M. Angelone, and M. Pillon, “Extreme ultraviolet single-crystal diamond detectors by chemical vapor deposition,” Appl. Phys. Lett. 86(19), 193509 (2005). [CrossRef]
26. M. Liao, Y. Koide, and J. Alvarez, “Single Schottky-barrier photodiode with interdigitated-finger geometry: application to diamond,” Appl. Phys. Lett. 90(12), 123507 (2007). [CrossRef]
27. H. C. Xuan, X. M. Wen, X. Yang, F. Bo, T. J. Zhi, and D. Y. Jian, “Highly narrow-band polarization-sensitive solar-blind photodetectors based on β-Ga2O3 single crystals,” ACS Appl. Mater. Interfaces 11(7), 7131–7137 (2019). [CrossRef]
28. W. Y. Kong, G. A. Wu, K. Y. Wang, T. F. Zhang, Y. F. Zou, D. D. Wang, and L. B. Luo, “Graphene-β-Ga2O3 heterojunction for highly sensitive deep UV photodetector application,” Adv. Mater. 28(48), 10725–10731 (2016). [CrossRef]
29. A. S. Pratiyush, S. Krishnamoorthy, S. V. Solanke, Z. Xia, R. Muralidharan, S. Rajan, and D. N. Nath, “High responsivity in molecular beam epitaxy grown β-Ga2O3 metal semiconductor metal solar blind deep-UV photodetector,” Appl. Phys. Lett. 110(22), 221107 (2017). [CrossRef]
30. Y. Qu, Z. Wu, M. Ai, D. Guo, Y. An, H. Yang, L. Li, and W. J. Tang, “Enhanced Ga2O3 /SiC ultraviolet photodetector with graphene top electrodes,” J. Alloys Compd. 680(25), 247–251 (2016). [CrossRef]
31. B. Zhao, F. Wang, H. Chen, L. Zheng, L. Su, D. Zhao, and X. Fang, “An ultrahigh responsivity (9.7 mA W−1) self-powered solar-blind photodetector based on individual ZnO-Ga2O3 heterostructures,” Adv. Funct. Mater. 27(17), 1700264 (2017). [CrossRef]
32. D. Y. Guo, H. Liu, P. Li, Z. Wu, S. Wang, C. Cui, C. Li, and W. Tang, “Zero-power-consumption solar-blind photodetector based on β-Ga2O3 /NSTO heterojunction,” ACS Appl. Mater. Interfaces 9(2), 1619–1628 (2017). [CrossRef]
33. X. Chen, K. Liu, Z. Zhang, C. Wang, B. Li, H. Zhao, D. Zhao, and D. Shen, “Self-powered solar-blind photodetector with fast response based on Au/β-Ga2O3 nanowires array film Schottky junction,” ACS Appl. Mater. Interfaces 8(6), 4185–4191 (2016). [CrossRef]
34. P. Li, H. Shi, K. Chen, D. Guo, W. Cui, Y. Zhi, S. Wang, Z. Wu, Z. Chen, and W. Tang, “Construction of GaN/ Ga2O3 p-n junction for an extremely high responsivity self-powered UV photodetector,” J. Mater. Chem. C 5(40), 10562–10570 (2017). [CrossRef]
35. A. Kanika, G. Neeraj, K. Mahesh, and K. Mukesh, “Ultrahigh performance of self-powered β-Ga2O3 thin film solar-blind photodetector grown on cost-effective Si substrate using high-temperature seed layer,” ACS Photonics 5(6), 2391–2401 (2018). [CrossRef]
36. X. Q. Ling, H. W. Ze, Y. Z. Yi, Z. L. Xing, and R. L. Yan, “Ultrahigh-responsivity, rapid-recovery, solar-blind photodetector based on highly nonstoichiometric amorphous gallium oxide,” ACS Photonics 4(9), 2203–2211 (2017). [CrossRef]
37. W. Y. Weng, T. J. Hsueh, S. J. Chang, G. J. Huang, and H. T. Hsueh, “A β-Ga2O3 solar-blind photodetector prepared by furnace oxidization of GaN thin film,” IEEE Sens. J. 11(4), 999–1003 (2011). [CrossRef]
38. K. K. Min, J.-Y. Kim, H. K. Baek, Y. C. Chu, C. B. Clare, and J. P. Seong, “Surface-plasmon-enhanced light-emitting diodes,” Adv. Mater. 20(7), 1253–1257 (2008). [CrossRef]
39. M. P. Imogen, D. K. Daniel, J. F. Arthur, and A. A. Harry, “Plasmonic nanoparticle enhanced photocurrent in GaN/InGaN/GaN quantum well solar cells,” Appl. Phys. Lett. 96(15), 153501 (2010). [CrossRef]
40. Y. W. Jyh, J. T. Fu, J. H. Jeng, Y. C. Cheng, L. Nola, W. K. Yean, and C. C. Yang, “Enhancing InGaN-based solar cell efficiency through localized surface plasmon interaction by embedding Ag nanoparticles in the absorbing layer,” Opt. Express 18(3), 2682–2694 (2010). [CrossRef]
41. A. Ragip, J. W. Pala, B. Edward, L. John, and L. B. Mark, “Design of plasmonic thin-film solar cells with broadband absorption enhancements,” Adv. Mater. 21(34), 3504–3509 (2009). [CrossRef]
42. A. A. Yu, K. Ostrikov, and E. P. Li, “Surface plasmon enhancement of optical absorption in thin-film silicon solar cells,” Plasmonics 4(2), 107–113 (2009). [CrossRef]
43. N. Keisuke, T. Katsuaki, and A. A. Harry, “Plasmonic nanoparticle enhanced light absorption in GaAs solar cells,” Appl. Phys. Lett. 93(12), 121904 (2008). [CrossRef]
44. W. Xiao, L. Kewei, C. Xing, H. L. Bing, M. J. Ming, Z. Z. Zhen, F. Z. Hai, and Z. S. De, “Highly wavelength-selective enhancement of responsivity in Ag nanoparticle-modified ZnO UV photodetector,” ACS Appl. Mater. Interfaces 9(6), 5382–5391 (2017). [CrossRef]
45. B. L. Da, J. S. Xiao, S. Hang, M. L. Zhi, R. C. Yi, J. Hong, and Q. M. Guo, “Realization of a high-performance GaN UV detector by nanoplasmonic enhancement,” Adv. Mater. 24(6), 845–849 (2012). [CrossRef]
46. D. H. Zheng, Y. W. Wen, J. C. Shoou, F. H. Yuan, J. C. Chiu, and Y. T. Tsung, “Ga2O3/GaN-based metal-semiconductor-metal photodetectors covered with Au nanoparticles,” IEEE Photonics Technol. Lett. 25(18), 1826–1828 (2013). [CrossRef]
47. J. C. Shu, X. M. Zeng, N. H. Yao, H. S. Mu, S. C. Quan, L. L. Hui, H. Z. Yong, D. B. Xue, and L. D. Xiao, “Surface plasmon enhanced solar-blind photoresponse of Ga2O3 film with Ga nanospheres,” Sci. China Phys. Mech. Astron. 61(9), 107021 (2018). [CrossRef]
48. Z. Wei, X. Jin, Y. Wei, L. Yang, Q. Q. Zhi, N. D. Jiang, H. W. Zhi, Q. C. Chang, Y. J. Jun, H. J. Li, and Y. F. Yan, “High-performance AlGaN metal–semiconductor–metal solar-blind ultraviolet photodetectors by localized surface plasmon enhancement,” Appl. Phys. Lett. 106(2), 021112 (2015). [CrossRef]
49. X. H. Hou, H. D. Sun, S. B. Long, G. S. Tompa, T. Salagaj, Y. Qin, Z. F. Zhang, P. J. Tan, S. J. Yu, and M. Liu, “Ultrahigh-performance solar-blind photodetector based on α-phase-dominated Ga2O3 film with record low dark current of 81 fA,” IEEE Electron Device Lett. 40(9), 1483–1486 (2019). [CrossRef]
50. Y. Qin, H. D. Sun, S. B. Long, G. S. Tompa, T. Salagaj, H. Dong, Q. M. He, G. Z. Jian, Q. Liu, H. B. Lv, and M. Liu, “High-performance mental-organic chemical vapor deposition grown ɛ-Ga2O3 solar-blind photodetector with asymmetric Schottky electrodes,” IEEE Electron Device Lett. 40(9), 1475–1478 (2019). [CrossRef]
51. X. H. Chen, Y. Xu, D. Zhou, S. Yang, F. F. Ren, H. Lu, K. Tang, S. L. Gu, R. Zhang, Y. D. Zheng, and J. D. Ye, “Solar-blind photodetector with high avalanche gains and bias-tunable detecting functionality based on metastable phase a-Ga2O3 / ZnO isotype heterostructures,” Appl,” ACS Appl. Mater. Interfaces 9(42), 36997–37005 (2017). [CrossRef]
52. L. Dain, H. Euyheon, L. Youngbin, C. Yongsuk, L. Seungwoo, and H. C. Jeong, “Multibit MoS2 photoelectronic memory with ultrahigh sensitivity,” Adv. Mater. 28(41), 9196–9202 (2016). [CrossRef]
