Self-Integrated Hybrid Ultraviolet Photodetectors Based on the

Research Article Cite This: ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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Self-Integrated Hybrid Ultraviolet Photodetectors Based on the Vertically Aligned InGaN Nanorod Array Assembly on Graphene Yulin Zheng,† Wenliang Wang,*,†,‡ Yuan Li,† Jianyu Lan,§ Yu Xia,† Zhichao Yang,† Xiaobin He,§ and Guoqiang Li*,†,‡ †

State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China Guangdong Choicore Optoelectronics Co. Ltd., Heyuan 517003, China § State Key Laboratory of Space Technology, Shanghai Institute of Space Power Sources, Shanghai 200245, China Downloaded via OCCIDENTAL COLG on March 28, 2019 at 04:46:56 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

‡

S Supporting Information *

ABSTRACT: Integration of one-dimensional (1D) semiconductors with two-dimensional (2D) materials into hybrid systems is identified as promising applications for new optoelectronic and photodetection devices. Herein, a selfintegrated hybrid ultraviolet (UV) photodetector based on InGaN nanorod arrays (NRAs) sandwiched between transparent top and back graphene contacts forming a Schottky junction has been demonstrated for the first time. The controlled van der Waals epitaxy of the vertically aligned InGaN NRA assembly on graphene-on-Si substrates is achieved by plasma-assisted molecular beam epitaxy. Moreover, the self-assembly formation mechanisms of InGaN NRAs on graphene are clarified by theoretical calculations with first-principles calculations based on density functional theory. The peculiar 1D/2D heterostructure hybrid system-based integrated UV photodetector simultaneously exhibits ultrafast response time (∼50 μs) and superhigh photosensitivity (∼105 A/W). It is highly believed that the concept proposed in this work has a great potential and can be widely applied for the next-generation integrated 1D/2D nano-based optoelectronic and photodetection devices. KEYWORDS: 1D/2D hybrid system, self-integrated UV photodetector, InGaN nanorod arrays, van der Waals epitaxy, first-principles calculations

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INTRODUCTION Van der Waals heterostructures incorporating two-dimensional (2D) materials and one-dimensional (1D) semiconductor materials integrated into hybrid systems open a new vista for the investigation of various emerging properties as well as applications for next-generation optoelectronic and photodetection devices.1−4 InGaN semiconductors in 1D nanorods (NRs) have recently been the focus of extensive research because of their superior properties caused by unique nanostructure-induced quantum confinement effects, such as enhanced carrier mobility,5 excellent optical absorption/ emission,6 and nearly free dislocation density.7 In this regard, InGaN NRs have been extensively fabricated into lightemitting diodes,8,9 photodetectors (PDs),5,10 field-effect transistors,1,11 laser diodes, and so forth.12 Among these optoelectronic devices, 1D nanostructurebased PDs have revealed outstanding promise owing to their ultrafast, supersensitive photoresponse engendered by two aspects. On the one hand, the huge surface-to-volume ratio significantly increases optical absorption and enhances the photogenerated carrier density.13 On the other hand, the lowdimensional nanostructure confines the active area of the charge carrier and reduces the transit time.14 Despite © XXXX American Chemical Society

enormous potential and achievement for these individual 1D nano-based PDs, the device processing and monolithic integration of such nanostructure arrays are rather complicating. 15 Conventional strategies are mainly focused on planarization of the nanostructured device by filling the gaps in the NR arrays (NRAs) with an insulating polymer16 or coalescing the top of NRAs during the deposition,15 which, however, may introduce dislocations and thus limit the performance of the device. On this stage, the integration as well as simple and efficient microfabrication is probably the most challenging of the 1D nano-based PDs. An intriguing route is to use a 2D graphene as a flexible and transparent top/ back contact material for integration and also as a seed layer substrate for 1D semiconductor NRA growth in this configuration. Because it was first exfoliated from graphite by Geim and Novoselov,17 graphene has rapidly raised on the horizon of materials science by virtue of its exceptionally properties,18−20 such as excellent electrical conductivity,18 supreme optical transparency,19 broad spectrum range,20 Received: January 15, 2019 Accepted: March 20, 2019 Published: March 20, 2019 A

DOI: 10.1021/acsami.9b00940 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces

Figure 1. Schematic for the fabrication process of an integrated hybrid graphene/InGaN NRAs/graphene UV PD.

Figure 2. (a) Time-resolved photocurrent response of integrated graphene/InGaN NRAs/graphene GSG Schottky contact UV PDs under 5 and 3 kHz pulsed UV light at a bias of 1 V. The magnified photocurrent response curve of the rising and falling edges under (b) 5 and (c) 3 kHz. (d) Typical I−V curves of the device in the dark and under 380 nm UV light illumination with a power density of 5 μW/cm2, and (e) the light densitydependent I−V curves of the device. (f) Spectral photon-response of the responsivity and EQE of the device under the illumination of light near the UV-A range (340−500 nm) at a bias of 1 V. (g) Photoresponsivity of the device as a function of light power density at a bias of 1 V.

mechanical flexibility,17 and so forth, which makes it a viable candidate for advanced photodetection devices. However, one issue of poor optical absorption of graphene limits the responsivity of purely graphene-based PDs.21 Combining graphene with 1D semiconductor NRAs, which has been proved to be of excellent optical absorption property, would effectively improve the sensitivity of photodetection.1,3,4 However, the detailed integration of InGaN NRA assembly

on graphene arising from van der Waals interactions for hybrid PDs has not been investigated in previous research, limiting the fundamental understanding of the 1D/2D van der Waals interaction hybrid systems and their applications. In this work, a self-integrated graphene/1D semiconductor/ graphene (GSG) Schottky junction is first formed for ultraviolet (UV) PDs where the InGaN NRAs are sandwiched between transparent top and back graphene contacts [Figure B


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Table 1. Summary of Key Photoresponse Parameters of 1D Nano-Based UV PDs in This Work and in Previous Reports description

light of detection (nm)

Ion/Ioff ratio

Rλ (A/W)

EQE (%)

∼102 203 3.4 × 104 101 11 ∼103 ∼103

2.7 × 104, ∼1.6 × 105 2.2 × 104 1.7 × 107 0.131 6.4 × 104 773 0.003 0.187

1.0× 107, ∼6.0 × 107 3.2 × 107 6.0 × 109 50 2.2 × 107 2.7 × 105 1.5 87.6

∼10

0.039 4.0 × 104 5.1 × 103

14.0 1.5 × 107 2.5 × 106

graphene/InGaN NRAs/graphene nonpolar GaN NW bicrystalline GaN NW GaN MWA/Si Pt−GaN NW bare GaN NW bare GaN NW MoS2/GaN films

380

3 × 104

325 360 325 380 380 365 265

graphene/ZnO NRAF bare ZnO MR bare Zn2GeO4 NW

380 325 260

rise/fall time 47.7/71.4 μs (5 kHz), 50.8/88.7 μs (3 kHz) 97% [Figure S2]. These UV photons with the energy above the band gap of InGaN are absorbed immediately, and electron−hole pairs are generated in the InGaN NRAs/ graphene interfaces.27 When a bias is applied, a strong built-in electric field is formed, which leads to the band bending in the depletion region, Figure 3c [where the reverse-biased Schottky barrier height (Φr) get heightened and the forward-biased Schottky barrier height (Φf) get lowered]. The built-in field promptly separates the photogenerated electron−hole pairs and sweeps electrons and holes toward the forward- and reverse-biased graphene electrodes, respectively. Therefore, the

The spectral responsivity (Rλ) and external quantum efficiency (EQE) are generally regarded as crucial parameters to quantify the photodetection performances and optoelectronic conversion efficiency of a dthe evice.4,13,14 Rλ and EQE can be estimated using the following equations,4,5 respectively Rλ =

Iphoto − Idark

EQE =

PillumS hc Rλ eλ

where Iphoto and Idark are the photocurrent and the dark current, respectively. Pillum and S are the light power density and the irradiated area of a PD device, respectively. The spectral response curve of Rλ and EQE for the device is measured at a bias of 1 V in the wavelength range of 340−500 nm, Figure 2e. Based on the equations mentioned above, it is found that the calculated Rλ and EQE reach the maximum value of 2.7 × 104 A/W and 1.0 × 107%, respectively, with the peak wavelength located at 380 nm. Accordingly, the curves illustrate that there is nearly a 104 times increase at 380 nm compared to at 500 nm, which is indicative of highly “visible-blind” of the PD device. This wavelength response selectivity stems from the inherent band gap of the InGaN materials in opposition to graphene with a zero band gap,18 which are also demonstrated by the room-temperature photoluminescence (PL) spectrum. Moreover, it is known that Rλ and EQE depend firmly on the light power density.5 The photocurrent rises from 2.7 to 15.0 μA [Figure 2d], while the calculated Rλ falls in the ranges of 2.7 × 104 to 0.88 × 104 A/W as the device is irradiated under the power density from 5 to 80 μW/cm2, as depicted in Figure 2f. The decrease of the Rλ with the increase of light power density may be attributed to the photogenerated charge saturation and trapping.11 In addition, we find that the Rλ of the device enhances linearly as the applied bias increases in the ranges of 1−5 V and rises to 1.6 × 105 A/W at 5 V [Figure S4]. Such linear relation implies that higher photoresponsivity can be easily achieved by simply increasing the applied bias.27 This superior responsivity of our device comes from higher D


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Figure 4. TEM images for the InGaN NR assembly on graphene-on-Si substrates at (a) low-magnification (overall view of NR) and (b) highmagnification (InGaN NR/graphene/Si hetero-interfaces), where carbon atomic columns of graphene are clearly resolved. (c) Simulated atom structure diagram for the InGaN NR assembly on graphene-on-Si substrates. (d) EDX line scan plots of Ga, In, C, and Si for InGaN NR/graphene/ Si heterostructures. (e) TEM image of the upper part for the InGaN NR, where the white-dashed arrow points toward the growth direction; and (f) is the magnified TEM image from the yellow square region in (e); the inset is the corresponding SAED patterns. (g) Room-temperature PL spectrum (excited by a 325 nm He−Cd laser)9 of the InGaN NRA assembly on graphene-on-Si substrates.

photocurrent is measured.14 Meanwhile, the reverse-biased Φr would be relatively lowered with the separation of photogenerated carriers [Figure 3d], which leads to a significant increase for the carrier density of the PD device, and concurrently, the lowered Φr allows the tunneling effects, which both enhance the measured photocurrent.28 The integrated GSG InGaN NRA PDs which own incalculable individual InGaN NR PD effectively provide countless parallelphotogenerated carrier transmission channels. In this regard, all these aforementioned are responsible for the high responsivity of the device. Upon turning off incident UV light, photogenerated carriers rapidly decrease and demonstrate shorter transit time which is derived from the particularly narrowed depletion layer width (which is approximately consistent with the average length of InGaN NRAs of ∼280 nm, Figure S6), therefore, significantly increasing the response speed of PDs.14 Because the feasibility of the high-performance integrated hybrid GSG UV PDs is ascribed to the peculiar 1D/2D heterostructure hybrid systems, it is noteworthy to focus in the following on the InGaN NRA assembly on graphene-on-Si substrates. The interfacial properties of InGaN NR/graphene/ Si heterostructures are first revealed by high-resolution transmission electron microscopy (HRTEM) characterizations.38−40 The overall view of vertically aligned InGaN NR demonstrates a length of ∼280 nm and a width of 60−90 nm for NR, Figures 4a and S6. Then, the cross-section HRTEM image, illustrated in Figure 4b, reveals that the region of TLG with a thickness of ∼1.2 nm can be identified underneath InGaN NR, where the carbon atomic columns are defined on account of the atoms located on the same horizontal dash line. 4 1 The out-of-plane epitaxial relationship of InGaN(0001)//Si(111) can be determined according to the crystal lattice.42 In addition, selected area electron diffraction (SAED) and X-ray diffraction (XRD) 2θ−ω scan curves are further adopted to illustrate the structural information and overall directional alignment for InGaN NRAs on the

graphene-on-Si substrate of InGaN(0001)//Si(111) and InGaN(101̅0)//Si(21̅1̅),42,43 Figures S7a and S8, respectively, which are consistent with the HRTEM image and the simulated atom structure constructed by the DFT framework, Figure 4c. Notably, the HRTEM image, Figure 4b, also reveals the sharp and abrupt hetero-interface, implying low-density dislocations, which thus, enhances the crystalline quality of subsequent InGaN NR.40 Furthermore, the energy-dispersive X-ray spectrometry (EDX) line scan profile evaluates the elemental concentration distribution across InGaN NR/ graphene/Si heterostructures,39 Figure 4d, which further supports HRTEM image results. Moreover, it is observed that graphene layers are partly distorted after InGaN NR growth, possibly due to the etching by the impinging nitrogen species22 during the PA-MBE growth, which would be discussed as follows. The crystalline structural properties of InGaN NR are also studied by HRTEM characterizations.6,39,40 The HRTEM image shows the apparent lattice fringes for the upper part of InGaN NR, and the integrated lattice for NR without detectible defects can be revealed as well, Figure 4e,f. As expected, an interplanar spacing of ∼0.5214 nm can be derived in the axial direction that is related to the (0001) spacing of the wurtzite InGaN lattice structure.6 Based on the interplanar spacing calculations from the HRTEM image and its corresponding SAED patterns, Figure S7b, In and Ga contents in InxGa1−xN NRAs can be determined as In0.05Ga0.95N.6,44 The EDX point analysis profile also confirms the elemental composition in the InGaN alloy, Figure S9, which is coincident. Moreover, the EDX composition mapping of In and Ga further exhibits the excellent uniform distribution of In and Ga elements in NRAs, Figure S10, suggesting the stable lattice structure and high crystalline quality.44 Finally, roomtemperature PL spectrum measurement for InGaN NRAs is employed to examine the optical properties,13 Figure 4g. It can be recognized that a narrow and intense peak centered at 380 nm and a wide and extremely weak green emission band which E


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Figure 5. (a) Mean Raman spectra of TLG and MLG transferred on Si substrates before the NRA growth. (b) Typical AFM image for TLG/Si heterostructures; inset, the line profile illustrates TLG with a thickness of ∼0.9 nm. SEM images of the InGaN NRA assembly on different substrates: (c) TLG- and (d) MLG-on-Si substrates, respectively. Mean Raman spectra of (e) TLG- and (g) MLG-on-Si substrates before and after growth, respectively. The comparison of the Raman intensity of the graphene 2D-peak position before and after growth for (f) TLG- and (h) MLGon-Si substrates, respectively. Schematic structure of lattice defective (i) TLG- and (j) MLG-on-Si substrates, respectively, where pseudohydrogens are introduced to terminate the dangling bonds of the slab.50 (k) Calculated adsorption energies of the most stable site on TLG- and MLG-on-Si surfaces for In, Ga, and N adatoms, illustrated in (i,j). (l) Migration energies of the most stable site on TLG- and MLG-on-Si surfaces for In and Ga adatoms.

[Figure 5b, inset] reveals the thickness of TLG of ∼0.9 nm, which is in well agreement with the HRTEM results. To clearly interpret the effect of graphene on the selfassembly formation mechanisms of InGaN NRAs, InGaN NRAs on TLG- and MLG-on-Si substrates with a distinct morphology and dimension are exhibited by scanning electron microscopy (SEM) images, Figure 5c,d, respectively. SEM images present different distributions of NRAs in density. Interestingly, the density of the NRA assembly on TLG- and MLG-on-Si substrates is statistically obtained as approximately 1.2 × 1010 and 4.0 × 109/cm2, respectively, which reflects that nucleation sites in TLG are larger than those in MLG at the initial growth stage. The distinct morphologies of InGaN NRAs on TLG- and MLG-on-Si substrates, as well as the electrical conductivity of graphene, result in the different device performances (dark current, Figure S11), which are discussed as follows. Note that the nucleation features of GaN nanowires (NWs) on graphene by PA-MBE were already reported,22 which concludes that nucleating preferentially occurs at morphological defects of graphene. Raman spectra [Figure 5a] have previously elucidated that the morphological defects of TLG and MLG by the determination of ID/IG of ∼0.06 and 0.04, that is, the morphological defects of TLG are slightly more than those of MLG. The self-assembly formation mechanisms for InGaN NRAs on TLG- and MLG-on-Si substrates are also associated with the impact of the PA-MBE growth on graphene layers. Accordingly, the variations of morphological defects of TLG and MLG after growth are detailedly explored by Raman spectroscopy, Figure 5e−h. For TLG, the ID/IG slightly

is related to quantum confinement Stark effect emission,9,45 further confirming the nearly free defects of InGaN NRAs. The 380 nm emission peak is thought to be the near band-edge emission of InGaN NRAs,9 which is consistent with the response wavelength of the PD device. In view of the results and discussion mentioned above, it is noticeable to perceive that graphene has great influence on the growth and properties of InGaN NRAs and on the performance of PD devices. Therefore, detailed analyses for TLG/ and MLG/Si heterostructures have been carried out. First, the underlying graphene in the 1D/2D heterostructure hybrid systems has been identified by Raman spectroscopy, Figure 5a, which displays the D, G, and 2D characteristic modes of graphene around 1357.2, 1578.2, and 2696.4 cm−1,4,46,47 respectively. Note that all Raman spectra data were obtained by means of mean spectra detected from randomly chosen spots of sample surfaces. It is known that the the 2D to G ratio (I2D/IG) corresponds to the layer number of graphene,48 and the D to G ratio (ID/IG) is sensitive to the morphological defects of graphene.47 Accordingly, the I2D/IG for the red/blue curves of ∼0.42/1.20 in Figure 5a confirms that TLG/MLG has been successfully transferred on Si substrates, respectively, and the ID/IG of ∼0.06/0.04 implies the persistence and high quality of graphene after the transfer. To further investigate the surface morphology of typical TLG/Si heterostructures before NRA growth, atomic force microscopy (AFM) was performed, as shown in Figure 5b. The uniform network of the surface with less wrinkles can be recognized which corresponds to the distinctive surface of graphene.49 AFM line profile analysis F


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ACS Applied Materials & Interfaces increases from ∼0.06 to ∼0.11, while the ID/IG grows from ∼0.04 to ∼0.37 for MLG after growth. The reduction of ID/IG indicates that the deposition of InGaN NRAs by PA-MBE introduces defects in graphene, and the underlying reason may result from the impinging nitrogen plasma during nitrogen RF supplying.22 Notably, the ID′/IG′ for MLG (∼0.37) is extremely higher than that for TLG (∼0.11), demonstrating that MLG has suffered greater damage compared with TLG after growth. Furthermore, the Raman spectra of the characteristic graphene 2D peak for TLG and MLG [Figure 5f,h] exhibit the comparison of spectral positions, intensities, and linewidths before and after growth. Expectedly, for TLG, the 2D peak maintains almost the same shape with unchanged positions at 2695.6 cm−1, and I2D is slightly down ∼6% after growth. In contrast, for MLG, a blue shift of the 2D peak can be noted (from 2696.4 to 2700.5 cm−1), which is attributed to the strain and/or lattice distortion in the graphene;38 and I2D is dramatically down ∼35% after growth, indicating the reduction of C−C sp2 bonding of graphene.22,38 In view of the fact that the damage of graphene is related to the intensity of ionized active N plasma which relies on the RF power applied and the N2 flow,22 we have chosen 400 W and 2.00 sccm as the best growth condition40 to suppress the etching of graphene, meanwhile, without losing the nucleation capability of InGaN. Moreover, the electrical conduction property of graphene is evaluated. It is well known that the full width at half-maximum (FWHM) of the 2D peak is strongly sensitive to the electronic mobility of the graphene,4,51 and a higher electrical conductivity of graphene generally has a smaller FWHM of the 2D peak.51 For TLG, Figure 5f, the FWHM maintains 34.5 cm−1 after growth, indicating almost unchanged electronic mobility of graphene. However, for MLG, Figure 5g, the FWHM rises from 31.3 to 48.1 cm−1 after growth, revealing a drastically reduction of the electronic mobility of graphene. The device performance (dark current) for integrated GSG InGaN NRA PDs based on both TLG- and MLG-on-Si substrates also embodies this depression [Figure S11]. Finally, to theoretically explore the self-assembly growth mechanism for InGaN NRAs on TLG and MLG-on-Si substrates, first-principles calculations based on the DFT framework were implemented. Theoretical calculations reveal that the adsorption and migration of InGaN precursor atoms on TLG- and MLG-on-Si substrates at the initial growth stage.52 In order to perfectly conform to actual experimental conditions, optimized stoichiometric TLG/Si(111) and MLG/ Si(111) slab models with a little intentionally break of C−C sp2 bonds of graphene were constructed in Figure 5j,i, and employed in the following. The adsorption energies (Ead) for three adsorption sites [Figure S12] with a high symmetry on graphene are calculated (details can be seen in Supporting Information).53,54 It is known that Ead demonstrates the adsorption behavior of an adatom, thus a positive and large value of Ead corresponds to a stable adsorption model.54 Accordingly, the calculated mean Ead of the most stable site on TLG- and MLG-on-Si surfaces for In, Ga, and N adatoms are presented in Figure 5k. It is identified that Ead on TLG-on-Si substrates is much larger than those on MLG-on-Si substrates for all kinds of adatoms, which indicates that InGaN precursors are more likely to absorb on TLG-on-Si substrates compared with MLG-on-Si substrates. In addition, the mean Ead of the N adatom of 7.26/4.83 eV is the largest among all for TLG/ MLG-on-Si substrates, which means that N atoms would first

adsorb on the substrate.53 Moreover, the migration energies (Emi) of In and Ga adatoms on TLG- and MLG-on-Si substrates are also calculated to disclose the migration behavior of an adatom, and a low value of Emi is in favor of the nucleation via migration and incorporation.55 It is observed that the mean Emi for In/Ga adatoms on TLG-on-Si substrates (54/82 meV) are much lower than those on MLG-on-Si substrates (209/241 meV), which are in agreement with the conclusions of Emi calculations. Theoretical calculations reveal that InGaN precursors are more likely to nuclear and incorporate on TLG-on-Si substrates compared with MLGon-Si substrates, which proves the SEM and Raman analyses.

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CONCLUSIONS To summarize, we report on a novel concept of self-integrated hybrid graphene/InGaN NRAs/graphene UV PDs for the first time through direct van der Waals epitaxy of InGaN NRAs on graphene-on-Si substrates by PA-MBE. The integrated PDs exhibit ultrafast response time (less than 50 μs, which is superior or comparable to the best result among all of the state-of-the-art 1D nano-based UV PDs); superhigh photosensitivity (Rλ and EQE ranging from 2.7 × 104 to 1.6 × 105 A/W and 1.0 × 107 to 6.0 × 107%, respectively); highly “visible-blind” of wavelength response selectivity; and superior photoresponse repeatability and stability. The excellent performance of the GSG UV PDs can be attributed to the utilization of the peculiar 1D/2D heterostructure hybrid systems. On the one hand, graphene used as the transparent and charge-sensitive electrodes enhances the light-harvesting, photoresponse, and stability of the device because of its highly optical transparency, excellent carrier mobility, and stable dangling bond-free 2D structure. On the other hand, InGaN NRAs integrated into one PD device has the following advantages: (1) NRAs provide myriad parallel photogenerated carrier channels for improved photocurrent; (2) NRAs enhance the optical absorption and sensitivity of photodetection of the device considering their huge surface-tovolume ratio and vertically aligned, dense, and high crystalline quality nanostructure arrays; (3) NRAs reduce the transit time of photogenerated carriers owing to the 1D quantum confinement for the narrowed depletion layer of the electron−hole pairs. Furthermore, the controlled operation of 1D/2D van der Waals heterostructures is achieved derived from the improvement of the morphological and structural properties of the InGaN NRAs. It is demonstrated that NR nucleation occurs more easily in TLG-on-Si than that in MLGon-Si at the initial growth stage, and MLG has suffered greater damage compared with TLG after growth. Therefore, by the utilization of TLG and the optimization of the growth condition, the formation of InGaN NRAs and the etching of graphene are well controlled and balanced. Meanwhile, the self-assembly formation mechanisms for InGaN NRAs on TLG- and MLG-on-Si substrates are theoretically studied by first-principles calculations based on DFT through calculating Ead and Emi. It is revealed that InGaN precursors are more likely to nuclear and deposit onto the TLG-on-Si surface because of their larger Ead and lower Emi compared with those on the MLG-on-Si surface. Consequently, the works of synthesizing and optimizing the InGaN NRA assembly on graphene does enable the fabrication of integrated hybrid 1D/ 2D-based UV PD devices. The self-integrated hybrid graphene/InGaN NRAs/graphene UV PDs have immense potential for the development of next-generation integrated G


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1D/2D hybrid-based optoelectronic and photodetection devices because of their outstanding performance.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.9b00940. Experimental methodssection, details of DFT calculations, additional SEM and TEM images of transferred MLG and InGaN NRAs, transmittance spectrum of graphene, additional photoresponsivity of PD device, evolution of the responsivity and photocurrent of PDs device, additional SAED patterns, XRD 2θ−ω scan curve, EDX analyses for InGaN NRAs, additional dark current for TLG- and MLG-based PDs, and schematic diagram of the graphene surface (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (W.W.). *E-mail: [email protected] (G.L.). ORCID

Guoqiang Li: 0000-0002-1493-6657 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is financially supported by the National Natural Science Foundation of China (grant nos. 51702102, 51602105, 51572091 and 51577070), National Science Fund for Excellent Young Scholars of China (grant no. 51422203), Natural Science Foundation of Guangdong Province (grant nos. 2017A030313331 and 2017A030310518), National Defense Scientific and Technological Innovation Special Zone (grant no. 17-163-13-ZT-008-029-04), National Natural Science Foundation Major Instrument Special Project of China (grant no. 51727901), and Source Fund of State Key Laboratory of Space Technology.

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