Graphene Interdigital Electrodes for Improving Sensitivity in a Ga2O3

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Functional Inorganic Materials and Devices

Graphene interdigital electrodes for improving sensitivity in Ga2O3:Zn deep-ultraviolet photoconductive detector Yuqiang Li, Dan Zhang, Richeng Lin, Zhaojun Zhang, Wei Zheng, and Feng Huang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b14380 • Publication Date (Web): 06 Dec 2018 Downloaded from http://pubs.acs.org on December 6, 2018

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ACS Applied Materials & Interfaces

Graphene interdigital electrodes for improving sensitivity in Ga2O3:Zn deep-ultraviolet photoconductive detector Yuqiang Li, Dan Zhang, Richeng Lin, Zhaojun Zhang, Wei Zheng, Feng Huang* State key Laboratory of Optoelectronic Materials and Technologies, School of Materials, Sun Yat-sen University, Guangzhou 510275, P. R. China ABSTRACT Graphene (Gr) has been widely used as a transparent electrode material for photodetectors due to its high conductivity and high transmittance, in recent years. However, the currently low-efficiency manipulation of Gr has hindered the arraying and practical use of such detectors. We invented a multistep method of accurately tailoring graphene into interdigital electrodes, for fabricating a sensitive, stable deep-ultraviolet photodetector based on Zn-doped Ga2O3 films. The fabricated photodetector exhibits a series of excellent performance, including extremely low dark current (~10-11 A), ultra-high photo-to-dark ratio (>105), satisfactory responsivity (1.05 A/W) and excellent selectivity for DUV band, compared to those with ordinary metal electrodes. The raising of photocurrent and responsivity is attributed to the increase of incident photons through Gr, and separated carriers caused by the built-in electric field formed at the interface of Gr and Ga2O3:Zn films. The proposed ideas and methods of tailoring Gr can not only improve the performance of devices, but more importantly, it contributes to the practical development of graphene.

KEYWORDS: graphene interdigital electrodes, photodetector, deep ultraviolet, gallium oxide, ultralow dark current

INTRODUCTION Deep-ultraviolet photodetector (DUVPD) has attracted substantial attention in space detection, atmosphere monitoring, biological science, etc.1-4 Among various potential semiconductor materials (such as ZnO, GaN, TiO2, SnO2) for high-performance DUVPD, Ga2O3 is considered as the most promising candidate.5 Such superiority of Ga2O3 originates from its direct-ultrawide bandgap (~4.8 eV), good thermal stability, and ~8 MV/cm critical electric field induced by the bandgap.6 In most practical applications, an imaging ability of photodetectors (PDs) is required. Thus, a fabrication technique of PD with arraying potential is significant, and those only prepared for unit device have no promising prospect for functional use. Obviously, the widely-reported nano Ga2O3-PDs show somewhat significance in science, but are fraught with big challenges for device arraying, due to the poor repeatability and size-uncontrollability of current nanotechnology.7, 8 According to the traditional crafts, arrayed PDs usually should be fabricated on large scale films.9 In the two common device structures with arraying ability, lateral metalsemiconductor-metal (MSM) PD constructs all electrodes on the same side of photosensitive layers (PSLs), highly compatible with the conventional microfabrication process.10, 11 Such MSM geometry 1

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also possesses a unique advantage of easier fabrication, compared to the other vertical sandwich structure (such as p-i-n PD with electrodes on two sides of PSL).12 Apparently, the same-sided metal electrodes of MSM PD will block the incident light, leading to an intrinsic low responsivity.4 Finding and assembling a DUV transparent electrode for PDs is likely to partially solve this problem. One might think the commonly used transparent electrode materials (such as ITO13, IZO14) may take effect. Actually, their bandgap are too narrow, thus the DUV will be strongly absorbed when their thicknesses exceed 10nm.15 While a very thin ITO film is deposited on PSLs, its resistance will be too large to be an effective electrode. Fortunately, the recently-researched graphene gives researchers an opportunity to satisfy the high requirements of the above MSM PD’s electrodes. Graphene possess an inherent high carrier mobility, despite composed of several or even monolayer carbon atoms.16 As we know, the transmittance of single layered carbon atoms is surely good enough to promise an ideal PD’s transparent electrode.17 Thus, developing a repeatable technique for integrating graphene onto PSLs and manipulating Gr via traditional microfabrication crafts, is key to developing new-generation arrayed PDs. At present, several works about combining Gr with Ga2O3 have been reported.2, 10, 18 Based on such progress, we concentrate more efforts on achieving accurate tailoring of Gr, to promote the application of it. Here, we report a method with arraying ability to bind graphene to Ga2O3 films by using a transfer technology. We thoughtfully selected highly-Zn-doped Ga2O3 films which have deep-level defects to obtain ultra-low dark current and establish a built-in electric field between Ga2O3 and graphene. Such a charge redistribution is beneficial for intrinsic electrostatic adsorption, making Gr endurable to lift off process in traditional crafts, and 10µm pitch interdigital monolayer graphene electrodes were prepared. As expected, a MSM solar-blind PD were successfully obtained. This PD exhibits high detectivity (4.9×1011 Jones), outstanding photo-to-dark ratio (＞105 ) and good spectral selectivity, and the dark current is effectively limited to 10-11 A. These satisfactory results with innovative method are beneficial to practical use of Gr, and may enlighten the researchers dedicated to various new-generation photoelectronic devices.

RESULTS AND DISCUSSION Based on MOCVD (metal organic chemical vapor deposition) grown Zn-doped Ga2O3 films, DUVPDs with graphene interdigital electrodes (GIEs) were successfully fabricated, by adopting the transfer method19 and microfabrication technology to accurately tailor graphene. Figure 1a is a schematic diagram of the device preparation process. From the details given in the schematics, it can be seen that the GIEs were prepared following the metal pad electrodes (Ti/Au 15 nm/80 nm) which are used for probe testing. An ohmic contact between Gr and Ti/Au are confirmed (Figure S1). One of the key steps in the preparation of GIEs is that the photoresist are creatively used as a secondary mask and we skillfully combined graphene tailoring with plasma etching. Such creation can not only achieve highprecision (micron-level) processing of graphene graphs, but also avoid the occurrence of plasma bypassing physical masks, thereby ensuring graphene electrode patterns intact without breakage. Figure 1b shows the GIE patterns on the SiO2 surface. The electrodes are clear and clean, without short or open circuits, or residual excess graphene. Further, the overall transfer of graphene and metal electrodes can reduce the limitation of substrates on the device preparation, allowing a wider application of graphene 2


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electrodes. Flexible support material PMMA can be utilized to realize such transfer (shown in Figure 1a). Figure 1c is an optical photograph of the Ga2O3:Zn DUVPD obtained after electrodes transferring. The GIEs are composed of 25 pairs finger with 10 μm width, 10 μm gap and 500 μm length. Several graphene fingers are not clear enough, due to the nature inhomogeneity of commercially available graphene itself and its low contrast with the Ga2O3:Zn films. Optical images of the photodetector with metal interdigital electrodes (MIEs) are shown in Figure S2.

Figure 1. Fabrication process and optical images of Ga2O3:Zn DUVPDs with GIEs. a) Schematic illustration of the preparation process. At the first step, graphene (Gr) is transferred onto SiO2 surface of the Si substrate by commonly used wet transfer method. Ti/Au electrodes which are used for probe testing are deposited on Gr by magnetron sputtering after standard photolithography process. Finally, both metal and Gr electrodes are transferred onto Ga2O3:Zn film by a facile method (see details in experimental section) with poly-methyl merthiolate (PMMA). b) Optical images of GIEs on SiO2 surface. c) Optical image of the DUVPD fabricated on Ga2O3:Zn films.

Understandably, device performance is affected by not only the fabrication process and device structure, but also the materials quality. The reported work not merely includes innovative and systematic device preparation methods, and also high-quality materials, which has been confirmed by various characterizations. Figure 2 presents a series of characterizations of Ga2O3:Zn films. The films are deposited on c-plane sapphire at 800° C with N2O as the oxygen source. Such high-temperature and weak oxidizing oxygen source growth condition has ensured a good crystal quality.20 The scanning electron microscopy (SEM) image of Ga2O3:Zn films in Figure 2a reveals a smooth surface of Ga2O3:Zn, indicating its high crystal quality. The uniform 340 nm thick Ga2O3:Zn films can be clearly observed in cross-sectional SEM morphology, as shown in Figure 2b. Figures 2c-e show the element maps of Ga, Zn, O respectively, and each reveals a uniform element distribution, indicating that the films are well3



regulated for growth and doping. The atomic force microscopy scanning result of a micrometer scaled area, as shown in Figure 2f, once again confirms its ultrasmooth surface. All these characterization results show good quality and smooth surface of the prepared films, which are highly significant for high-performance devices.

Figure 2. Characterization of Ga2O3:Zn films deposited on c-plane sapphire substrate by MOCVD. a) SEM image of the Ga2O3:Zn films and a smooth surface is clearly observed. b) The cross-sectional SEM morphology of the films. The thickness is 340 nm, which is noted in the figure. c-e) Element maps of Ga, Zn, and O, revealing a high uniformity of the grown Ga2O3:Zn films. f) AFM image of the Ga2O3:Zn films, the root mean square (RMS) of roughness is 4.9 nm, showing a smooth surface.

For a thorough analysis of the device, we characterized Ga2O3:Zn/Gr DUVPD with micro-Raman spectroscopy, XRD (X-ray diffraction), EDS (energy dispersive spectrometer) and optical absorption spectrum. From the Raman study shown in Figure 3a, it can be seen that the phonon peaks of Ga2O3:Zn are located in the scope of 100-800 cm-1. The peaks near 100 cm-1 and 200 cm-1 are related to the lowfrequency vibration of atoms in Ga2O3:Zn, and those of 300-500 cm-1 formed by mid-frequency deformation are overlapped by the strong peaks of sapphire21. The inset shows a peak around 643 cm-1, which mainly originates from the high-frequency stretching and bending of the GaO4 tetrahedron.10 The observed Raman peaks are consistent with previous theoretical calculations and experimental results,2226 indicating the complete lattice with few defects of Ga O :Zn films. In addition, Raman spectroscopy 2 3 4


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is also a powerful method to characterize graphene. For Gr, a weak D peak, and strong G and 2D peaks can be observed from the Raman spectrum. The D peak relates to the defects of Gr, thus the relative intensity ratio of peak D to G can be used to represent the Gr’s defect level. The ID/IG and I2D/IG values are 0.26 and 1.49, respectively, suggesting that the graphene electrodes have few defects.27 Figure 3b is the XRD pattern of the Ga2O3:Zn films, where the inset is a corresponding EDS spectrum. The characteristic peaks of Ga2O3:Zn are observed from the figure respectively, and the FWHM of (-201) peak is merely 0.12°, confirming its good crystallinity again28. The atomic percentage of Zn element obtained by EDS is 9.96%, which contributes to the small amount of ZnGa2O4 phase appearing in the XRD pattern. From the optical absorption spectrum (Figure 3c), it can be seen that there is an obvious absorption cut-off edge near the wavelength of 250 nm, which is consistent with the results of the optical transmission spectrum (Figure S3). The bandgap of the prepared films can be roughly estimated to be 5.1eV (Figure 3c inset), based on its relationship with absorption coefficient, which is in line with the requirement of photosensitive materials for DUVPDs.

Figure 3. a) Raman scattering pattern of the DUVPDs. Characteristic signals of components Ga2O3:Zn (blue label), Gr (red label) and Al2O3 (black label) are all observed. The Raman peak of 643 cm-1 of Ga2O3:Zn is also shown in the inset. b) XRD pattern of the film, (-201), (-402), (-603) peaks of Ga2O3:Zn are observed at 18.91°, 38.32°, and 59.11°, respectively. The FWHM of (-201) peak is only 0.12°, exhibiting good crystal quality. (551) peak of ZnGa2O4 is also observed at 57.73°. The EDS map (inset) reveals the At.% of O (58.97%), Zn (9.96%), Ga (31.07%), respectively. c) Absorption spectrum of Ga2O3:Zn; the inset is the plot of (αhν)2 as a function of photon energy (hν); α is the absorption coefficient. 5



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The I-V characteristics of the photodetectors with GIE or MIE in dark and 254 nm illumination, respectively, are plotted in Figure 4a. It can be seen that the GIE detector has the same extremely low dark current as the conventional MIE one (1.6 ×10-11 A at 5 V bias), whereas its photocurrent has been promoted by more than one order of magnitude (5.3×10-6 A with GIE, 2.7×10-7 A with MIE). The symmetrical currents under positive and negative bias are derived from the back-to-back junction in the device. The vertical cross-section of this PD and simple circuit schematic can be seen from Figure S4. This suggests the dark current is successfully limited to a very low level by Zn element doping, and meanwhile the photocurrent is promoted by graphene’s high carrier mobility and high transmittance to DUV light.29, 30 According to the report, Gr allows about 90% of DUV incident light to reach the PSL to excite photogenerated carriers.17 Moreover, the GIE photodetector also exhibits an ultrahigh phototo-dark ratio (Ilight/Idark) with a numerical value exceeding 105, demonstrating an excellent switching ability. High switching ratio and low dark current are critical to practical photodetectors,31 and the comparison of such parameters in Ga2O3 or Ga2O3/Gr photodetectors can be seen in Table 1. Table 1. Comparison of Performance Parameters in Ga2O3 Photodetectors material

dark current (A)

photo-to-dark ratio

Graphene/β-Ga2O3

1.1×10-6

R (A/W)

rise time

decay time

Ga2O3/NSTO

-2.56×10-8

β-Ga2O3

3×10-10

β-Ga2O3

340

1.48

94.83 s

219.19 s

2

20

43.31

0.07 s

0.21

32

13.3

0.62 s

0.83/8.14 s

33

1.28×10-7

11.4

0.86

1.02/16.61 s

34

β-Ga2O3

1.4×10-12

>103

96.13

32 ms

78 ms

35

β-Ga2O3/ZnO

2.9×10-10

~16.7

0.35

1.02/11.66 s

0.62/7.84 s

36

1.6×10-11

3.31×105

1.05

4.5 s

2.2 s

this work

Graphene/β-Ga2O3/ Graphene

references

Also, it can be seen from the figure that the photocurrent will increase with bias voltage, because at higher bias, the drift speed of photocurrent will increase and photogenerated carriers’ recombination will be suppressed.37, 38 Figure 4b compares the time-resolved photoresponse performance of the two photodetectors at 5V bias, and both exhibit fast response and decay. When the 254 nm illumination was repeatedly switched on or off, the GIE photodetector maintained a good stability. The response and decay time of this detector is divided into 4.5 s and 2.2 s, which is not as fast as the conventional ones, but relatively fast among the currently reported Gr/Ga2O3 detectors.2, 10, 18 The photocurrent increases with growing light power density (Figure 4c), and the inset gives an approximately linear dependence between them. Such dependence originates from the increased photocarriers (i.e. electron-hole pairs) excited by increased light power, which brings higher photocurrent. Long carrier transport distance in MSM PD and low carrier mobility caused by doping are the main reasons for slow response time. To evaluate the selectivity of this GIE photodetector, the spectral response from 200 to 300 nm was measured at 5 V bias and shown in Figure 4d, where the spectral measurement step is 2 nm. It can be seen that the detector is highly sensitive to photons with wavelength below 260 nm, and there is almost no response to light above 260 nm, which is consistent with the optical absorption spectrum described in Figure 3c, exhibiting outstanding DUV selectivity. Here, the slow rise of photocurrent in spectral response is mainly attributed to the remnant photoconductive effect of devices, which coincides with 6


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the phenomenon that occurred in the time-resolved photoresponse measurement. Similar phenomenon has also been observed in the other reported works,2, 10 but detailed investigation is onging. Apart from the remnant photoconductive effect, the seeming low responsivity in the initial stage of spectrum response is also influenced by the small facula area used in this test, which cannot cover the whole device’s active area. The inset of Figure 4d compares the responsivity of the two type detectors at the same light intensity. The responsivity of the GIE detector is 1.05 A/W at 5 V, which is over one order of magnitude higher than that of the MIE one, demonstrating GIE's significant improvement in device performance. The responsivity of devices can be calculated by the following formulas:39, 40 𝐼𝑝ℎ𝑜𝑡𝑜 𝜇𝜏𝑉𝜂𝑡𝑟𝑎𝑛𝑠𝜂𝑎𝑏𝑠𝑒𝜆 R= = 𝐴 ∙ 𝑃𝑖𝑛𝑐 𝐿2ℎ𝑐 Iphoto is the photocurrent (5.3×10-6A), A the active area of the device (1×1.12 mm2), and Pinc the incident light power density (457.8μw/cm2). The latter equation is specifically defined for photoconductive detectors, describing how each microscopic parameter affects R (where μ refers to carrier mobility, τ carrier recombination lifetime, V applied bias, ηtrans current transfer efficiency, ηabs light absorption coefficient, e electronic charge, λ wavelength of incident light, L gap of electrodes, c velocity of light and h Planck constant). Detectivity D* is another important indicator for evaluating the performance of detectors. It comprehensively considers thermal effects, breakdown current, carrier recombination, and other factors. The D* of GIE detectors in this work is 4.9×1011 Jones, which is determined by the relationship:2 𝑅 𝐷∗ = 2𝑒𝐼𝑑𝑎𝑟𝑘/𝐴 R refers to the detector's responsivity (1.05 A/W), e the electronic charge, and Idark the dark current (1.6×10-11A).

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Figure 4. a) I-V characteristics of the fabricated DUVPDs under dark and illumination (254 nm) for different situations: Gr interdigital electrodes (GIE) or metal interdigital electrodes (MIE). b) Time-dependent photocurrent of above two PDs measured at room temperature at 5 V bias under illumination of 254 nm light. The rise time is defined to be 10% 90% of the Imax and the decay time is defined to be 90% - 10% of the Imax. c) I-V characteristics of the Gr PDs with light power density from 10. 3 to 328.8 μw/cm2. The inset shows the photocurrent is linearly dependent on irradiance intensity. d) Spectral response of the GIE DUVPDs at 5 V bias. The inset shows the photoresponsivity versus applied voltage for the PDs with GIE or MIE, under the illumination of 254 nm light with 328.8 μw/cm2.

The GIE DUVPD also exhibits a very large external quantum efficiency (EQE) of 5.12×102 % at 5 V bias under 254 nm illumination, which is defined as the number of electrons generated per incident photon and can be obtained by the equation:41 𝑅ℎ𝑐 EQE = 𝑒𝜆 Where h denotes Planck's constant, c the light speed, and λ the wavelength of incident light. The large EQE indicates a large optical gain inside the device. It can be seen from Figure 5 that the GIE PD exhibits good stability or linear dependence on light power density at different voltages, wherein the EQE almost unchanged versus it, and the photocurrent has a linear relationship with the light power density. It can be seen from the above formula that the change of EQE only depends on R under the condition of the incident wavelength λ fixed. Figure 4c shows that the photocurrent is almost linearly dependent on the light power, so it is known from the equation R=Iphoto/A.Pinc that R does not change with Pinc, and this is why EQE has almost unchanged. The relationship between responsivity and light 8


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power can be seen from Figure S5. The electrical characterization shows that, under the careful tailoring and preparing, graphene interdigital electrodes do play a role superior to the metal electrodes in effectively improving the detectors’ photocurrent and responsivity, meanwhile maintaining the good stability, which further advances the practical use of graphene. The GIE PDs even perform very well after being placed in ambient condition for six months (Figure S6).

Figure 5. The dependence of GIE PD s’ photocurrent and EQE on light power density at different bias, a) 3 V, b) 5 V. Blue square label represents photocurrent, corresponding to the left coordinate axis; and red sphere label represents EQE, corresponding to the right coordinate axis. Blue solid lines are the fitting results of linear dependence between photocurrent and light power density. The light source used to characterization is 254 nm.

The operating mechanism of the DUVPD can be illustrated by the energy band diagram in Figure 6, which is one of the two symmetrical junctions. When Gr is in contact with Ga2O3:Zn films, the electrons in the latter will drift toward Gr, correspondingly, the energy band near Ga2O3:Zn bends upward at the interface, forming an energy barrier and creating a built-in electric field (depletion region), and the builtin potential is deduced to be around 0.68 eV based on the reported works.42-44 The barrier hinders the migration of electrons under dark conditions, making the dark current restricted in a low level. When irradiated by deep ultraviolet light (254 nm), the Ga2O3:Zn will absorb photons to excite electrons from its valence band to conduction band, forming electron-hole pairs. Subsequently, under the action of the built-in electric field, photogenerated electron-hole pairs are separated and moved to the opposite direction (electrons toward Ga2O3:Zn, and holes toward Gr). Depending on the well-designed device structure, the carriers are separated vertically and transported laterally, and such separation contributes to a longer carrier lifetime, improving the photocurrent of the DUVPD (Figure S7). This photoelectric process only happens when the incident light’s energy is higher than the bandgap of Ga2O3:Zn, which is also the essential reason for the spectral selectivity in Figure 4c.

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Figure 6. Energy band diagram of the Gr/Ga2O3:Zn heterojunction.

CONCLUSIONS In this work, traditional microfabrication technology was used to realize the expected tailoring and transfer of graphene, and the GIEs were successfully prepared. Combining with Ga2O3:Zn materials, we demonstrated a MSM DUVPD with good selectivity to the deep UV band. The device exhibits extremely low dark current (1.6×10−11 A at 5 V bias), ultrahigh photo-to-dark ratio (more than 105 ), and great optical gain (EQE reaches 5.12 ×102 %). The promotion of device performance by GIE is significant. Compared to the MIE detectors, the responsivity of GIE photodetector is improved by one order of magnitude, reaching 1.05 A/W at a bias voltage of 5 V, which is relatively high among largesized photodetectors. All these results indicate that the fabricated detectors have great potential for future applications. In addition, the reported work provides a technique to design and tailor graphene on semiconductor substrates deliberately, and it not only have significance on device performance, but also provide inspiration and reference for boosting graphene-based detectors developing into arrayed ones.

METHODS Thin Film Growth Epitaxial Ga2O3:Zn films were deposited on c-plane sapphire at 800 °C by using MOCVD, and the reaction chamber pressure was about 250 Torr. N2O, triethylgallium (TEGa) and diethylzinc (DEZn) were adopted as growth precursors. Graphene Transfer First, an anisole solution (Wt. % of PMMA is 5%) was prepared as a support material for the transfer process, and it was stirred at 70° C until become clear and transparent. The graphene was grown on copper sheet, and was available commercially. Then, PMMA was spin-coated onto the Gr surface, dried, and afterwards the Gr/copper sheet was put into a solution of 0.1 mol/L ammonium persulfate, soaking for a complete dissolution of the copper. Finally, the Gr was transferred to the SiO2 surface of the Si substrate by the intermolecular force, and the PMMA was removed by acetone, ethanol and deionized water in sequence. 10


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Preparation of GIEs An interdigital photoresist mask was prepared on the surface of the graphene layer by using a photolithography technique. Afterwards, excess graphene was etched away by plasma for 90 seconds, and the photoresist was removed with acetone to obtain GIE. Electrodes Transfer The prepared PMMA solution was spin-coated on the electrodes surface of SiO2, dried at 70°C for 10 minutes, and soaked in a 4 mol/L NaOH solution for 15 minutes to etch the SiO2 layer. Then, both graphene and metal electrodes supported by the PMMA were fully mechanically exfoliated with thermal release tape (released at 130 °C), and the PMMA was removed in the above same manner after transferring onto the Ga2O3:Zn substrates by intermolecular force. Device Characterization The structure and crystalline quality of the Ga2O3:Zn films were characterized by PANalytical Xray Diffractometer. The chemical composition and cross-sectional morphology measurements were performed by ZEISSAURIGA Focused Ion Beam etching system. The surface morphology and optical properties of the film were characterized by atomic force microscopy CSPM 5500 and UV-VIS spectrophotometer (Shimadzu UV-2500). The I-V characteristics of the device were measured by using Keithley 2636B source meter. The 254 nm monochromatic light was from the spectral line of a quartzpackaged low-pressure mercury lamp through a 254 nm optical filter, and the light power density was measured by the optical power meter of Ophir (NOVA II header and PD300-UV probe). The Raman spectrum pattern was characterized by Renishaw inVia reflex microRaman spectroscopy (with 514 nm pump laser). The DUV spectral-response test system used Shimadzu UV-2600 as continuous adjustable light source, with VXUV20A photodetector (PTO DIODE CORP) as light-power calibration and KEITHLEY 2636b as SourceMeter. The optical images were obtained by LEICA DM2700 M metalloscope. The photolithography process was implanted by CETC BG-401A photolithography system, and the plasma was generated by BYT PE500 RF Genetator.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ***. The ohmic contact between Gr and Ti/Au electrodes, optical image of DUVPD with MIE, transmission spectrum of Ga2O3:Zn films, dependence of GIE DUVPD’s photocurrent and responsivity on light power density on fixed bias, time-dependent photoresponse of GIE DUVPD after six months

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] ORCID Feng Huang: 0000-0002-4623-2216 Notes 11



The authors declare no competing financial interest.

ACKNOWLEDGEMENTS We acknowledge financial support from the National Natural Science Foundation (No. U1505252, 61604178, 91333207 and 61427901) and Guangzhou Science and Technology Program (No.201607020036).

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Heterojunction for Highly Sensitive Deep UV Photodetector Application. Adv.Mater 2016, 28 (48), 1072510731. 3.

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Graphene Interdigital Electrodes for Improving Sensitivity in a Ga2O3

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