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Abstract
We present a high-performance broadband (450-1550 nm) black phosphorus photodetector based on a thin-film lithium niobate waveguide. The waveguides are fabricated by the proton exchange method with flat surfaces, which reduces the stress and deformation of two-dimensional materials. At a wavelength of 1550 nm, the photodetector simultaneously achieves a high responsivity and wide bandwidth, with a responsivity as high as 147 A/W (at an optical power of 17 nW), a 3-dB bandwidth of 0.86 GHz, and a detectivity of 3.04 × 1013 Jones. Our photodetector exhibits one of the highest responsivity values among 2D material-integrated waveguide photodetectors.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Lithium niobate (LN) is a widely used material in the field of optoelectronics owing to its remarkable electro-optical (γ33 = 31 pm/V), acousto-optical, nonlinear, and piezoelectric properties, as well as its large transparent range (0.4-5 µm) [1–6]. With the development of ion cutting technology, the manufacturing of high-quality thin-film lithium niobate (TFLN) has become achievable [7]. Compared to traditional bulk LN, TFLN boasts a high refractive index contrast between the LN thin-film and SiO2, greatly improving the integration of photonic devices [8]. As a photonic chip platform, TFLN holds great potential and can be applied in various fields, such as those involving optical communication, micro- and nano- optoelectronic devices, and multifunctional photonic integration [9–17].
Photodetectors (PDs) are a crucial component of photonic circuits. TFLN cannot be directly used for the fabrication of PDs and requires heterogeneous integration with other materials [18–20]. Conventional semiconductor materials exhibit lattice mismatch with TFLN, making it impossible to directly grow these materials on the TFLN. Instead, a complex bonding process is needed. The emergence of two-dimensional materials (2DM) offers a solution to these problems of lattice mismatch [21,22]. 2DMs are thin-film materials composed of a single or few layers of atoms or molecules that can be obtained through mechanical exfoliation, liquid-phase assisted exfoliation, and chemical vapor deposition [23–25]. Their smooth surfaces can be linked to the substrate surface by van der Waals forces, resulting in high mobility and quantum efficiency [26–29].
In recent years, various 2DMs have been investigated for photodetection, including graphene, black phosphorus (BP), transition metal dichalcogenides, and others [30–34]. Moreover, there has been a significant increase in research efforts to construct heterojunction waveguide detectors using 2DMs across different optical material platforms [31,35,36]. For instance, the integration of graphene with silicon has demonstrated an extraordinary ultra-high response speed of 110 GHz. Additionally, the integration of BP with silicon has achieved a remarkable high responsiveness of 66 A/W and a response speed of 1.05 GHz. Likewise, the integration of MoS2 with silicon nitride has showcased a responsiveness of 15.7 mA/W and a bandwidth of 1.37 GHz. However, it is crucial to emphasize that research on waveguide photodetectors integrated on the TFLN platform remains relatively limited. Among the various 2D materials studied, BP is an ideal material for creating PDs on TFLN due to its exceptional optoelectronic properties and ease of integration with TFLN. The band gap of BP increases as the number of layers decreases, with a band gap in the range of 1.5 ∼ 0.3 eV for monolayer to bulk BP, corresponding to an ability to absorb light from visible to mid-infrared wavelengths [37–39]. Moreover, BP can achieve a carrier mobility of 10000 cm2/V·s and a picosecond relaxation time at room temperature, resulting in high-speed responsive characteristics [40].
A few types of 2DMs have already been used to integrate PDs on TFLN waveguides [20,41]. However, simultaneously achieving a high responsivity and wide bandwidth is still a challenging task. In this study, we propose and demonstrate a high responsivity and high-speed BP PD integrated with a proton-exchanged (PE) TFLN waveguide operating at wavelengths of 450-1550 nm. The 2DM BP with an appropriate thickness and size was transferred onto the flat surface of the PE waveguide. The photoelectric properties of the PD were demonstrated by testing the current-voltage (I-V) and current-time (I-T) curves, which showed a remarkably high responsivity of 147 A/W at a low bias voltage of 0.5 V. Furthermore, the PD exhibited a high 3-dB bandwidth of 0.86 GHz and a high detectivity of 3.04 × 1013 Jones.
2. Results
Figure 1(a) displays a three-dimensional structural diagram of the BP PD integrated with the TFLN waveguide, with the source and drain electrodes included. The electrodes were adjacent to the waveguide, reducing the transmission distance between them and shortening the response time. To improve the adhesion between the gold (Au) electrode and LN thin-film, a layer of chromium (Cr) was deposited underneath the Au layer. A scanning electron microscopy (SEM) image of the PE waveguide is shown in Fig. 1(b). The width of the waveguide was approximately 6 µm. Figure 1(c) shows a cross-sectional view of the PD, which included a BP layer, two Au/Cr electrodes, and a 6 µm-wide PE TFLN waveguide. The waveguide was formed by the PE method, which yielding a loss of 0.7 dB/cm and its smooth surface can reduce the deformation and internal stress of the 2DM [42].
Fig. 1. (a) Schematic diagram of the photodetector. (b) SEM image of the PE waveguide surface. (c) Cross-sectional view of the photodetector. (d) Optical microscope image of the BP covered on the TFLN waveguide. (e) AFM image of the BP covered on the LN waveguide. (f) Raman spectra of BP under a 532 nm laser.
Figure 1(d) is an optical microscope image of the BP PD, which shows that the BP was aligned along the waveguide direction with a length of approximately 56 µm and bonded to the waveguide by van der Waals forces. Figure 1(e) shows a map of the thickness of the BP 2DM characterized by atomic force microscopy (AFM), which confirmed the material thickness to be approximately 20 nm. The white spots on the image are water that was absorbed on the BP surface during testing. Figure 1(f) displays the Raman spectra of multilayer BP collected with an excitation laser of 532 nm. Three prominent peaks were observed at approximately 365, 440, and 470 cm−1, which corresponded to the A1g, B2g, and A2g characteristic vibration modes, respectively [43]. The B2g and A2g modes corresponded to the in-plane vibration modes of the phosphorus atoms, while the A1g mode corresponded to the out-of-plane vibration mode of the phosphorus atoms [44].
To validate the feasibility of the experiment, we simulated the absorption values of BP on the PDs under varying conditions. The BP material exhibited anisotropy and could be categorized in the armchair (AC) and zigzag (ZZ) directions based on different crystal orientations. Since the peeled BP used in the experiment consisted of multiple layers, its performance was similar to that of bulk BP. To determine its refractive index, we calculated both the real (n) and imaginary (κ) refractive indexes of BP in the AC and ZZ directions using the Cauchy absorption model, as shown in the following formula: [45]
Figure 3(a) shows the simulated electric field distribution of the waveguide in the fundamental transverse electric (TE00) mode, in which the electric field is mainly concentrated in the waveguide. Figure 3(b) is the simulated electric field distribution of the TE10 mode in PE waveguide. To investigate the effect of the waveguide width in different modes on PD performance, we simulated the absorption loss of BP on waveguides with αAC and αZZ, corresponding to the absorption loss in the AC and ZZ directions parallel to the waveguide, respectively. The widths of waveguide ranging from 3 µm to 9 µm while maintaining a fixed PE depth of 230 nm. The results are shown in Fig. 3(c). The absorption loss of the metal electrodes (αm) is also presented in the Fig. 3(c) for comparison. The AC orientation exhibited considerably higher light absorption compared to the ZZ orientation. BP had a higher absorption than the electrodes, indicating that BP absorbed the majority of the optical energy. As the waveguide width increased, the electrode absorption decreased faster than that of BP. Besides, the results revealed that for waveguide widths smaller than 5 µm, only the TE00 mode was present, followed by the appearance of the TE10 mode, and then the TE20 mode emerged after 8 µm. All three modes exhibited similar behavior, showing a decrease in αm with an increase in waveguide width. This was primarily due to the electrodes moving further away from the center of the waveguide with increasing waveguide width, leading to reduced absorption. For the absorption of BP, there was a slight decrease before reaching a waveguide width of 6 µm, after which the level of absorption remained constant.
Fig. 3. Electric field distribution of the (a) TE00 mode and (b) TE10 mode in PE waveguide. (c) Absorption loss of BP and electrodes at different PE widths. (d) Absorption loss of BP and electrodes at different PE depths. (e) Absorption loss of BP in the AC and ZZ directions at different BP thicknesses.
The results shown in Fig. 3(d) verified the effect of the PE depth on absorption at a width of 6 µm. As depicted in the figure, BP exhibited almost consistent absorption within a PE depth range of 180-260 nm. The absorption loss by BP with different thicknesses above the waveguide was calculated. As depicted in Fig. 3(e), the absorption loss of BP increased with thickness. For a waveguide with a width of 6 µm, the absorption losses of BP were 0.45 dB/cm (AC direction) and 0.05 dB/cm (ZZ direction), which indicated that lengths of 7 µm (AC direction) and 60 µm (ZZ direction) were required to absorb half of the light energy.
The photoresponse of the fabricated PDs was evaluated by coupling a linearly polarized laser into the waveguide at different wavelengths using a conical lensed fiber under the test conditions of 293 K temperature and 50% humidity. Figure 4(a) shows the variation in the photocurrent (Ipc) with the bias voltage from 0 V to 0.5 V at a wavelength of 1550 nm, with laser input powers of P = 17 nW, 170 nW, 680 nW, 6.8 µW, and 34 µW. The Ipc was calculated by the following formula:
where I is the total current. Idark is the dark current of the PD which is shown in inset of Fig. 4(a). When the bias voltage was less than 0.5 V, the photocurrent of the PD increased linearly. The I-V curves for other wavelengths (450, 850, 1060 and 1310 nm) with bias voltages from 0 V to 0.5 V are presented in Supplement 1. It was obvious that a higher photocurrent could be obtained under high power than under low power. This indicated that our PD had a broadband optical response ranging from visible light to near-infrared light. The light switching response curves of the PD at different laser powers, corresponding to the photocurrent values in the I-V curve, were presented in Supplement 1.Fig. 4. Performance characterization of the PD operating under 1550 nm laser excitation. (a) Photocurrent as a function of bias voltage at different input laser powers. (b) Variation of photocurrent and responsivity with power at Vbias = 0.5 V. (Inset in (a) Dark current at Vbias = 0.5 V.)
Figure 4(b) shows the variation of photocurrent (orange) and responsivity (purple) with power at Vbias = 0.5 V. When the laser power was below 5 µW, the photocurrent increased rapidly with increasing laser power. However, as the power continued to increase, the increase in photocurrent gradually slowed down. Responsivity (R) is an important parameter in measuring PD performance and reflects the sensitivity of the PD to laser power, defined as:
where P is the power of laser. It can be observed that the responsivity decreased with increasing optical power. The responsivity was maximal at the lowest power (17 nW) with a value of 147.4 A/W, while it decreased to 1.77 A/W when the power gradually increased (e.g., 34 µW). This phenomenon occurred mainly because as the optical power increased, the number of charge carriers also increased. This further increased the possibility of charge carriers becoming trapped by defects in the material and increased the probability of electron–hole recombination. The combination of these two factors led to a decrease in responsivity [46]. As the 2 V bias approaches the detector's maximum tolerance, repeated testing risks damaging the detector. Consequently, to facilitate subsequent tests and avoid such damage, we selected a 0.5 V bias to characterize the photoelectric performance of the device. To further characterize the I-V characteristics of the photodetector at higher voltages, we tested another sample's I-V curves under bias voltages ranging from 0 to 2 V at 1550 nm, as shown in Supplement 1.The main working principle of the photodetector is the photoconductive effect. Figure 5 illustrates the energy band diagram under applied bias. When the laser is coupled into the waveguide, it is gradually absorbed by the black phosphorus. Photons excite electrons from the valence band to the conduction band, leaving behind holes in the valence band. The transition of electrons to the conduction band increases the carrier density, thereby enhancing the material's conductivity. Consequently, photocurrent is generated under bias conditions.
Detectivity (D) is another important parameter that is used to describe the performance of a detector, defined as the reciprocal of the noise equivalent power (NEP). We calculated the detectivity at a wavelength of 1550 nm to characterize the detector performance. The main sources of high-speed signal noise in a PD are shot noise (${I_{shot}} = \sqrt {2q{I_{dark}}} $) and Johnson noise (${I_{John}} = \sqrt {\frac{{4{k_B}T}}{R}} $), with shot noise being the predominant source. Therefore, we approximated the detectivity as follows:[47]
where the value of Idark at 0.5 V bias voltage and 293 K temperature is 73 µA. The calculated detectivity was 3.04 × 1013 Jones, indicating that the BP PD integrated with TFLN had strong detection capability.The frequency response of the PD working at 1550 nm was measured by using a 6.5 GHz vector network analyzer (VNA). Figure 6(a, b, c) shows the response frequency at different biases when the input power was 73 µW. To better describe the bandwidth of the device, a single pole low-pass filter mode was introduced to fit the data [48]. This model is widely used in bandwidth testing and allows only low-frequency signals from 0 Hz to the cutoff frequency to pass. The fitting formula was as follows:
where S and f are the normalized radio-frequency (RF) response and frequency, respectively. R and C are the resistance and capacitance of the device, respectively. The red dashed lines in Fig. 6(a, b, c) are the fitting lines, indicating the tendency of the frequency response. When the bias voltage was set to 0.5 V, the bandwidths was 0.34 GHz, and it reached saturation between 1.5 V to 2 V, with the bandwidth remaining at 0.86 GHz. RC-time and transit-time are two crucial factors that affect the bandwidth of a photodetector. To identify the limiting factors of our detector's bandwidth, we measured the capacitance-voltage curve of the photodetector (illustrated in Supplement 1) and calculated RC bandwidth by the formular ${f_{3dB}} = \frac{1}{{2\pi RC}}$. The calculated RC bandwidth is in the order of hundreds of MHz. Additionally, the saturation of capacitance observed between 1.5 V and 2 V aligns with the bandwidth test results. Thus, we can reasonably conclude that the bandwidth is indeed limited by the RC-time.Fig. 6. Frequency response at (a) Vbias = 0.5 V, (b) Vbias = 1.5 V and (c) Vbias = 2 V at a 73 µW power level.
Figure 7 shows a comparison of PDs heterointegrated with Si and LN waveguides [19,20,31,35,47,49–55]. Currently, research on Si-based PDs is more extensive, and they exhibit better performance. However, achieving both a high responsivity and wide bandwidth in PDs integrated with TFLNs poses certain difficulties. By heterointegrating PE TFLN waveguides with BP, we were able to simultaneously achieve both a high responsivity and high-speed characteristics. A responsivity of 147 A/W was achieved at a low bias voltage of 0.5 V, and a high response frequency of 0.86 GHz was also achieved.
Fig. 7. Comparative chart of the responsivity and 3-dB bandwidth values of heterointegrated PDs on SOI and TFLN waveguides, with corresponding references listed for each data point.
3. Conclusion
We integrated BP onto a PE TFLN waveguide to produce a PD and tested its performance under different wavelengths. The PE waveguide structure had a flatter surface, which reduced the stress and defects in the two-dimensional materials. In terms of performance, a high light response of up to 147.35 A/W and a 3-dB bandwidth of 0.86 GHz were obtained at 1550 nm, as well as a detectivity of 3.04 × 1013 Jones. This study verified the feasibility of PE TFLN waveguide-integrated PDs, achieved high-performance results, and demonstrated great development prospects in a large wavelength range, especially in the communication band.
4. Experimental methods
4.1 Device simulation
The full-vectorial finite difference method in the commercial software Lumerical: Mode Solutions was used to calculate the electric field distribution of the waveguide, as well as the absorption losses of the metal electrodes and BP.
4.2 Waveguide and electrode fabrication
The devices were made using a commercial x-cut TFLN wafer (NANOLN), where the device layer of 500 nm thickness was located on a SiO2/LN-stack substrate. A 70 nm thick Cr film and a 30 nm thick Au film were deposited on the TFLN by a lift-off process and vacuum thermal evaporation, serving as the mask for PE. The TFLN was then immersed in benzoic acid and heated at 170 °C for 3 mins to carry out PE, resulting in a PE layer with a depth of approximately 230 nm and a width of approximately 6 µm. The depth of the PE layer was determined by the prism-coupling method. The Au/Cr layer was also used as the electrode material, and the electrode pattern was formed again by photolithography. Then, the excess electrode material was separately corroded in Au and Cr etchants, resulting in electrodes with a length of 100 µm.
4.3 Transfer process of BP
The BP crystal was fabricated by chemical vapor transport (Shenzhen Six Carbon Technology). Red phosphorus and tin were ground into powder, and then the temperature of the quartz vacuum-sealed tube was increased to 600 °C for growing BP crystals. The transfer method for the BP layer involved using tape to peel off the 2DMs, which were then placed onto polydimethylsiloxane (PDMS). The material with a suitable size and thickness of approximately 20 nm was transferred to the appropriate position on the waveguide using a transfer platform. After heating at 80 °C, the PDMS became less adhesive, and the material adhered to the waveguide through van der Waals forces.
4.4 Measurement of optoelectronic properties
Semiconductor lasers with wavelengths of 1550 nm, 1310 nm, 1060 nm, 850 nm, and 450 nm were used as light sources, and an end-face coupling method was employed to couple the lasers to the waveguide through a single-mode fiber. The I-V curves of the PD were measured at different laser power levels by applying a bias voltage using a semiconductor parameter analyzer (Keithley 4200a-SCS). The I-T curve measurement setup is shown in Fig. S5(a) of Supplement 1. The function generator was used to control the laser and obtain a laser output with a period of 5 s. The photoresponse of the devices was measured at a bias voltage of 0.5 V, and the results were obtained using the semiconductor parameter analyzer. The capacitance-voltage curve was measured using a semiconductor parameter analyzer.
During the bandwidth test, a 1550 nm laser was modulated by applying a modulation voltage to a commercial LN Mach–Zehnder modulator using a VNA (Keysight E5071C). The electrical signal generated by the PD after receiving the modulated laser was received using an RF probe. Subsequently, the RF signal was sent back to the VNA to calculate the device frequency response. A bias tee was utilized to apply a bias voltage to the PD and prevent direct current (DC) signals from entering the VNA. A diagram of the measurement setup is illustrated in Fig. S5(b) of Supplement 1.
Funding
National Natural Science Foundation of China (12105190, 61935014, 12005147); Shenzhen Science and Technology Planning (JCYJ20190813103207106); SZTU Self-made Instrument & Equipment Project.
Acknowledgments
YouTian Hu: Investigation (lead); Methodology (lead); Data curation (lead); Writing-original draft preparation (lead); Software (lead). Fan Yang: Validation (supporting). Jiamin Chen: Validation (supporting). Shijia Lu: Validation (supporting). Huangpu Han: Writing-review and editing (supporting). Yujie Ma: Writing-review and editing (supporting). Zhigang Zhao: Validation (supporting). Guangyue Chai: Writing-review and editing (supporting). Bingxi Xiang: Conceptualization (lead); Methodology (lead); Writing-review and editing (lead); Supervision (lead); Funding acquisition (lead). Shuangchen Ruan: Writing-review and editing (supporting).
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
Supplemental document
See Supplement 1 for supporting content.
References
1. A. Boes, L. Chang, C. Langrock, M. Yu, M. Zhang, Q. Lin, M. Loncar, M. Fejer, J. Bowers, and A. Mitchell, “Lithium niobate photonics: Unlocking the electromagnetic spectrum,” Science 379(6627), eabj4396 (2023). [CrossRef]
2. Y. F. Qi and Y. Li, “Integrated lithium niobate photonics,” Nanophotonics 9(6), 1287–1320 (2020). [CrossRef]
3. A. Boes, B. Corcoran, L. Chang, J. Bowers, and A. Mitchell, “Status and Potential of Lithium Niobate on Insulator (LNOI) for Photonic Integrated Circuits,” Laser Photonics Rev. 12(4), 1700256 (2018). [CrossRef]
4. L. T. Cai, A. Mahmoud, M. Khan, M. Mahmoud, T. Mukherjee, J. Bain, and G. Piazza, “Acousto-optical modulation of thin film lithium niobate waveguide devices,” Photonics Res. 7(9), 1003–1013 (2019). [CrossRef]
5. F. Timpu, J. Sendra, C. Renaut, L. Lang, M. Timofeeva, M. T. Buscaglia, V. Buscaglia, and R. Grange, “Lithium Niobate Nanocubes as Linear and Nonlinear Ultraviolet Mie Resonators,” ACS Photonics 6(2), 545–552 (2019). [CrossRef]
6. A. V. Syuy, N. V. Sidorov, M. N. Palatnikov, D. S. Shtarev, E. A. Antonycheva, and A. Y. Gaponov, “Photoelectric fields in lithium niobate crystals,” Opt. Quantum Electron. 49(3), 126 (2017). [CrossRef]
7. Y. C. Jia, L. Wang, and F. Chen, “Ion-cut lithium niobate on insulator technology: Recent advances and perspectives,” Appl. Phys. Rev. 8(1), 011307 (2021). [CrossRef]
8. X. Zhenda and Z. Shining, “LiNbO3 crystals: from bulk to film,” Adv. Photon. 4(03), 030502 (2022). [CrossRef]
9. C. Wang, M. Zhang, X. Chen, M. Bertrand, A. Shams-Ansari, S. Chandrasekhar, P. Winzer, and M. Loncar, “Integrated lithium niobate electro-optic modulators operating at CMOS-compatible voltages,” Nature 562(7725), 101–104 (2018). [CrossRef]
10. M. He, M. Xu, Y. Ren, J. Jian, Z. Ruan, Y. Xu, S. Gao, S. Sun, X. Wen, L. Zhou, L. Liu, C. Guo, H. Chen, S. Yu, L. Liu, and X. Cai, “High-performance hybrid silicon and lithium niobate Mach–Zehnder modulators for 100 Gbits−1 and beyond,” Nat. Photonics 13(5), 359–364 (2019). [CrossRef]
11. S. Sun, M. He, M. Xu, S. Gao, S. Yu, and X. Cai, “Hybrid Silicon and Lithium Niobate Modulator,” IEEE J. Select. Topics Quantum Electron. 27(3), 1–12 (2021). [CrossRef]
12. M. G. Vazimali and S. Fathpour, “Applications of thin-film lithium niobate in nonlinear integrated photonics,” Adv. Photon. 4(03), 034001 (2022). [CrossRef]
13. G. Y. Chen, N. X. Li, J. D. Ng, H. L. Lin, Y. Y. Zhou, Y. H. Fu, L. Y. T. Lee, Y. Yu, A. Q. Liu, and A. J. Danner, “Advances in lithium niobate photonics: development status and perspectives,” Adv. Photon. 4(03), 034003 (2022). [CrossRef]
14. X. Liu, S. Gao, C. Zhang, Y. Pan, R. Ma, X. Zhang, L. Liu, Z. Xie, S. Zhu, S. Yu, and X. Cai, “Ultra-broadband and low-loss edge coupler for highly efficient second harmonic generation in thin-film lithium niobate,” Adv. Photon. Nexus 1(01), 016001 (2022). [CrossRef]
15. M. Yu, D. Barton Iii, R. Cheng, C. Reimer, P. Kharel, L. He, L. Shao, D. Zhu, Y. Hu, H. R. Grant, L. Johansson, Y. Okawachi, A. L. Gaeta, M. Zhang, and M. Loncar, “Integrated femtosecond pulse generator on thin-film lithium niobate,” Nature 612(7939), 252–258 (2022). [CrossRef]
16. G. Poberaj, H. Hu, W. Sohler, and P. Gunter, “Lithium niobate on insulator (LNOI) for micro-photonic devices,” Laser Photonics Rev. 6(4), 488–503 (2012). [CrossRef]
17. X. Sun, Y. Sheng, X. Gao, Y. Liu, F. Ren, Y. Tan, Z. Yang, Y. Jia, and F. Chen, “Self-Powered Lithium Niobate Thin-Film Photodetectors,” Small 18(35), 2203532 (2022). [CrossRef]
18. X. Zhang, X. Liu, R. Ma, Z. Chen, Z. Yang, Y. Han, B. Wang, S. Yu, R. Wang, and X. Cai, “Heterogeneously integrated III-V-on-lithium niobate broadband light sources and photodetectors,” Opt. Lett. 47(17), 4564–4567 (2022). [CrossRef]
19. X. W. Guo, L. B. Shao, L. Y. He, K. Luke, J. Morgan, K. Y. Sun, J. Y. Gao, T. C. Tzu, Y. Shen, D. K. Chen, B. T. Guo, F. X. Yu, Q. H. Yu, M. Jafari, M. Loncar, M. Zhang, and A. Beling, “High-performance modified uni-traveling carrier photodiode integrated on a thin-film lithium niobate platform,” Photonics Res. 10(6), 1338–1343 (2022). [CrossRef]
20. S. F. Wang, R. J. Chapman, B. C. Johnson, I. Krasnokutska, J. L. J. Tambasco, K. Messalea, A. Peruzzo, and J. Bullock, “Integration of Black Phosphorus Photoconductors with Lithium Niobate on Insulator Photonics,” Adv. Optical Mater. 11(2), 2201688 (2023). [CrossRef]
21. Z. Tang, S. Chen, D. Li, X. Wang, and A. Pan, “Two-dimensional optoelectronic devices for silicon photonic integration,” J. Materiomics 9(3), 551–567 (2023). [CrossRef]
22. N. Zhou, R. Yang, and T. Zhai, “Two-dimensional non-layered materials,” Mater. Today Nano 8, 100051 (2019). [CrossRef]
23. K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva, and A. A. Firsov, “Electric field effect in atomically thin carbon films,” Science 306(5696), 666–669 (2004). [CrossRef]
24. Z. Lin, Y. Liu, U. Halim, M. Ding, Y. Liu, Y. Wang, C. Jia, P. Chen, X. Duan, C. Wang, F. Song, M. Li, C. Wan, Y. Huang, and X. Duan, “Solution-processable 2D semiconductors for high-performance large-area electronics,” Nature 562(7726), 254–258 (2018). [CrossRef]
25. Z. Cai, B. Liu, X. Zou, and H. M Cheng, “Chemical Vapor Deposition Growth and Applications of Two-Dimensional Materials and Their Heterostructures,” Chem. Rev. 118(13), 6091–6133 (2018). [CrossRef]
26. Z. Cheng, R. Cao, K. Wei, Y. Yao, X. Liu, J. Kang, J. Dong, Z. Shi, H. Zhang, and X. Zhang, “2D Materials Enabled Next-Generation Integrated Optoelectronics: from Fabrication to Applications,” Adv. Sci. 8(11), 2003834 (2021). [CrossRef]
27. Y. C. Zhao, Y. Q. Su, Y. Q. Guo, and C. Z. Wu, “Intercalation-assisted Exfoliation Strategy for Two-dimensional Materials Preparation,” Chem. Res. Chin. Univ. 36(4), 518–524 (2020). [CrossRef]
28. Y. Zhang, Q. C. Liu, and B. X. Xu, “Liquid-assisted, etching-free, mechanical peeling of 2D materials,” Extreme Mech. Lett. 16, 33–40 (2017). [CrossRef]
29. X. Li, W. Cai, J. An, S. Kim, J. Nah, D. Yang, R. Piner, A. Velamakanni, I. Jung, E. Tutuc, S. K. Banerjee, L. Colombo, and R. S. Ruoff, “Large-area synthesis of high-quality and uniform graphene films on copper foils,” Science 324(5932), 1312–1314 (2009). [CrossRef]
30. W. Liu, J. H. Lv, L. Peng, et al., “Graphene charge-injection photodetectors,” Nat. Electron 5(5), 281–288 (2022). [CrossRef]
31. C. Y. Liu, J. S. Guo, L. W. Yu, Y. L. Xiang, H. T. Xiang, J. Li, and D. X. Dai, “High-Speed and High-Responsivity Silicon/Black-Phosphorus Hybrid Plasmonic Waveguide Avalanche Photodetector,” ACS Photonics 9(5), 1764–1774 (2022). [CrossRef]
32. S. Lu, J. Chen, F. Yang, H. Han, X. Li, L. Chen, Y. Wu, B. He, G. Chai, S. Ruan, and B. Xiang, “Surface plasmon-enhanced photodetection of monolayers MoS 2 on an ion beam modified functional substrate,” J. Appl. Phys. 132(18), 183102 (2022). [CrossRef]
33. Y. Ma, “Ultrathin SnSe2 flakes: a new member in two-dimensional materials for high-performance photodetector,” Sci. Bull. 60(20), 1789–1790 (2015). [CrossRef]
34. X. M. Wang, Z. Z. Cheng, K. Xu, H. K. Tsang, and J. B. Xu, “High-responsivity graphene/silicon-heterostructure waveguide photodetectors,” Nat. Photonics 7(11), 888–891 (2013). [CrossRef]
35. P. Ma, Y. Salamin, B. Baeuerle, A. Josten, W. Heni, A. Emboras, and J. Leuthold, “Plasmonically Enhanced Graphene Photodetector Featuring 100 Gbit/s Data Reception, High Responsivity, and Compact Size,” ACS Photonics 6(1), 154–161 (2019). [CrossRef]
36. Z. W. Li, S. Q. Hu, Q. Zhang, R. J. Tian, L. P. Gu, Y. S. Zhu, Q. C. Yuan, R. X. Yi, C. Li, Y. Liu, Y. Hao, X. T. Gan, and J. L. Zhao, “Telecom-Band Waveguide-Integrated MoS2 Photodetector Assisted by Hot Electrons,” ACS Photonics 9(1), 282–289 (2022). [CrossRef]
37. Z. Wu, Y. Lyu, Y. Zhang, R. Ding, B. Zheng, Z. Yang, S. P. Lau, X. H. Chen, and J. Hao, “Large-scale growth of few-layer two-dimensional black phosphorus,” Nat. Mater 20(9), 1203–1209 (2021). [CrossRef]
38. Y. Yi, Z. B. Sun, J. Li, P. K. Chu, and X. F. Yu, “Optical and Optoelectronic Properties of Black Phosphorus and Recent Photonic and Optoelectronic Applications,” Small Methods 3(10), 1900165 (2019). [CrossRef]
39. K. Wang, B. M. Szydlowska, G. Wang, X. Zhang, J. J. Wang, J. J. Magan, L. Zhang, J. N. Coleman, J. Wang, and W. J. Blau, “Ultrafast Nonlinear Excitation Dynamics of Black Phosphorus Nanosheets from Visible to Mid-Infrared,” ACS Nano 10(7), 6923–6932 (2016). [CrossRef]
40. J. Qiao, X. Kong, Z.-X. Hu, F. Yang, and W. Ji, “High-mobility transport anisotropy and linear dichroism in few-layer black phosphorus,” Nat. Commun. 5(1), 4475 (2014). [CrossRef]
41. Z. J. Yu, Y. Wang, B. L. Sun, Y. Y. Tong, J. B. Xu, H. K. Tsang, and X. K. Sun, “Hybrid 2D-Material Photonics with Bound States in the Continuum,” Adv. Optical Mater. 7(24), 1901306 (2019). [CrossRef]
42. L. Cai, R. Kong, Y. Wang, and H. Hu, “Channel waveguides and y-junctions in x-cut single-crystal lithium niobate thin film,” Opt. Express 23(22), 29211–29221 (2015). [CrossRef]
43. F. Xia, H. Wang, and Y. Jia, “Rediscovering black phosphorus as an anisotropic layered material for optoelectronics and electronics,” Nat. Commun. 5(1), 4458 (2014). [CrossRef]
44. S. Yu, Y. Du, X. Niu, G. Li, D. Zhu, Q. Yu, G. Zou, and H. Ju, “Arginine-modified black phosphorus quantum dots with dual excited states for enhanced electrochemiluminescence in bioanalysis,” Nat. Commun. 13(1), 7302 (2022). [CrossRef]
45. S. Y. Lee and K. J. Yee, “Black phosphorus phase retarder based on anisotropic refractive index dispersion,” 2D Mater. 9(1), 015020 (2022). [CrossRef]
46. T. Tong, Y. Chen, S. Qin, W. Li, J. Zhang, Z. Chunhui, C. Zhang, X. Yuan, X. Chen, Z. Nie, X. Wang, F. Wang, W. Liu, P. Wang, X. Wang, and Y. Xu, “Sensitive and Ultrabroadband Phototransistor Based on Two-Dimensional Bi2O2Se Nanosheets,” Adv. Funct. Mater. 29(50), 1905806 (2019). [CrossRef]
47. R. Maiti, C. Patil, M. A. S. R. Saadi, T. Xie, J. G. Azadani, B. Uluutku, R. Amin, A. F. Briggs, M. Miscuglio, D. Van Thourhout, S. D. Solares, T. Low, R. Agarwal, S. R. Bank, and V. J. Sorger, “Strain-engineered high-responsivity MoTe2 photodetector for silicon photonic integrated circuits,” Nat. Photonics 14(9), 578–584 (2020). [CrossRef]
48. N. Flory, P. Ma, Y. Salamin, A. Emboras, T. Taniguchi, K. Watanabe, J. Leuthold, and L. Novotny, “Waveguide-integrated van der Waals heterostructure photodetector at telecom wavelengths with high speed and high responsivity,” Nat. Nanotechnol. 15(2), 118–124 (2020). [CrossRef]
49. Y. Ma, B. Dong, J. Wei, Y. Chang, L. Huang, K.-W. Ang, and C. Lee, “High-Responsivity Mid-Infrared Black Phosphorus Slow Light Waveguide Photodetector,” Adv. Opt. Mater. 8(13), 2000337 (2020). [CrossRef]
50. N. Youngblood, C. Chen, S. Koester, and M. Li, “Waveguide-integrated black phosphorus photodetector with high responsivity and low dark current,” Nat. Photonics 9(4), 247–252 (2015). [CrossRef]
51. Y. Yin, R. Cao, J. Guo, C. Liu, J. Li, X. Feng, H. Wang, W. Du, A. Qadir, H. Zhang, Y. Ma, S. Gao, Y. Xu, Y. Shi, L. Tong, and D. Dai, “High-Speed and High-Responsivity Hybrid Silicon/Black-Phosphorus Waveguide Photodetectors at 2 µm,” Laser Photonics Rev. 13(6), 1900032 (2019). [CrossRef]
52. L. Huang, B. Dong, X. Guo, Y. Chang, N. Chen, X. Huang, W. Liao, C. Zhu, H. Wang, C. Lee, and K. W. Ang, “Waveguide-Integrated Black Phosphorus Photodetector for Mid-Infrared Applications,” ACS Nano 13(1), 913–921 (2019). [CrossRef]
53. C. Chen, N. Youngblood, R. Peng, D. Yoo, D. A. Mohr, T. W. Johnson, S. H. Oh, and M. Li, “Three-Dimensional Integration of Black Phosphorus Photodetector with Silicon Photonics and Nanoplasmonics,” Nano Lett. 17(2), 985–991 (2017). [CrossRef]
54. B. Desiatov and M. Loncar, “Silicon photodetector for integrated lithium niobate photonics,” Appl. Phys. Lett. 115(12), 121108 (2019). [CrossRef]
55. Y. Xue, X. X. Wu, K. X. Chen, J. J. Wang, and L. Liu, “Waveguide integrated high-speed black phosphorus photodetector on a thin film lithium niobate platform,” Opt. Mater. Express 13(1), 272–281 (2023). [CrossRef]
