- Email: [email protected]
InP MQWs electroabsorption modulator
Accepted Manuscript Title: Analysis and Optimization of 1.5-m InGaAsP/InP MQWs electroabsorption modulator Authors: Dai-bing Zhou, Song Liang, Hui-tao Wang, Wu Zhao, Rui-kang Zhang, Ling-juan Zhao, Wei Wang PII: DOI: Reference:
S0030-4026(19)30128-7 https://doi.org/10.1016/j.ijleo.2019.02.011 IJLEO 62338
To appear in: Received date: Revised date: Accepted date:
22 June 2018 21 December 2018 2 February 2019
Please cite this article as: Zhou D-bing, Liang S, Wang H-tao, Zhao W, Zhang R-kang, Zhao L-juan, Wang W, Analysis and Optimization of 1.5-m InGaAsP/InP MQWs electroabsorption modulator, Optik (2019), https://doi.org/10.1016/j.ijleo.2019.02.011 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Analysis and Optimization of 1.5-μm InGaAsP/InP MQWs electroabsorption modulator Dai-bing Zhou*, Song Liang, Hui-tao Wang, Wu Zhao, Rui-kang Zhang, Ling-juan Zhao, Wei Wang Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Science,
SC RI PT
College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, Beijing 100083, China.
Abstract: The effects of doping profile and well thickness on the light extinction properties of electroabsorption modulators (EAM) are studied experimentally. It is found that both light p type doping in the InP cladding layer and a large well thickness help to get higher extinction ratios at a given reverse bias voltage. A 3D EAM model has been built for optimizing the performance of EAMs. The simulation results are in a good agreement with the experimental results. With the optimized EAM designs, a modulator with an over 20 dB extinction ratio at a low bias voltage is demonstrated.
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Keywords: Electroabsorption modulator (EAM), Multiple quantum well (MQW), Extinction ratio.
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1. Introduction
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EAMs based on the Quantum Confined Stark Effect (QCSE) have been used in the optical fiber communication systems as important components, due to their low cost, compact size and easy integration with other devices [1-5]. To obtain a high absorption coefficient, EAM is normally designed to have quantum wells, which have larger thickness than barriers to achieve large extinction ratio (ER) under a low bias voltage [6,7]. But this cannot be realized when EAM is integrated with lasers by the selective area growth or identical active layer technology [8,9], in which both the EAM and laser multiple quantum wells (MQWs) are grown in the same epitaxy run. Different from EAMs, MQWs with thin wells are needed to obtain high performance lasers [10]. Normally, the p type dopant in the cladding layer of EAMs is Zn, which diffuses into the MQWs during the cladding layer growth, weakening the quantum confined Stark effect, and in turn deteriorating the EAM performance. Thus, the doping level in the cladding layer should be optimized to reduce the Zn diffusion while maintaining a low device resistance. In this work, we build a 3D EAM model to analyze the effects of Zn diffusion and well thickness of MQWs on the performance of EAMs [11-14]. The aim of this study is to analyze and optimize the performance of EAM by adjusting only a few parameters, making the performance of the EAMs suitable for application requirements. Several different types of EAM devices are fabricated by adjusting the p-type Zn doping distribution, which is measured by Secondary ion mass spectrometer (SIMS). By running the model with the measured Zn distribution, it is shown that the distribution of electric field in the active region is changed by the Zn diffusion into separate confinement heterostructure (SCH) layer, thus the quantum confined Stark effects is weakened. Then, we simulate and optimize the optical extinction efficiency of EAMs by changing the well thickness of MQWs. Optical transmission characteristics of the fabricated EAMs are in good agreement with the simulations. The ER performance of the EAM is enhanced and the driving voltage is reduced with a large well thickness.
2. Device Design and Fabrication In this study, the EAMs are designed into the three different types of structures. Type 1 EAM has the same MQW structure as type 2, but type 1 has higher p-type Zn doping concentrations than type 2 EAM. The p-type Zn doping
1
Thickness of type 1 and type 2 (nm)
Layer
Thickness of type 3 (nm)
Substrate
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concentration of type 3 is the same as type 2, but the quantum well thickness is increased by 30% compared to type 2, and the thickness of the SCH layer is decreased to 95.5 nm in order to have the same total thickness of the active layer. The three types of EAMs have the same fabrication process. The epitaxial layer structure of EAM is shown in Table 1. The EAMs were fabricated by the following procedures. First, an 800 nm InP buffer layer was grown on an n-type Si-doped InP substrate by metal organic chemical vapor deposition (MOCVD). Then, multiple quantum wells which consist six InGaAsP wells and seven InGaAsP barrier layers were grown, which were sandwiched between two InGaAsP SCH layers. The 20 oC photoluminescence (PL) wavelength of the MQWs is 1500 nm. Finally, a p-type InP cladding layer and InGaAs contact layer were grown. A 3-μm-wide ridge waveguide was formed by wet etching technology. Then, Ti/Au p-electrode was sputtered and patterned on the p-side of the device. After thinning the wafer to about 150 μm, Au/Ge/Ni n-electrode was deposited. The obtained EAMs are mounted on AlN heat sinks for measurements. Table 1．Epitaxial Material Structure Material
PL wavelength (nm)
n-InP n-InP
920
Lower SCH
100
95.5
i-InGaAsP
1200
Well
5
6.5
i-InGaAsP
1500
Barrier
10
10
i-InGaAsP
1200
Upper SCH
100
95.5
i-InGaAsP
1200
Cladding layer
1500
1500
p-InP
920
Contact layer
300
300
p-InGaAs
U
800
N
800
M
A
Buffer layer
ED
3. Effects of Zn Diffusion on Modulation Performance
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A tunable laser was used as a light source during the dc ER tests. TE polarized lights with different wavelengths were coupled into and out of the EA modulators by tapered single-mode fibers. The coupling efficiency between the chip and the single-mode fiber is 45%. In this study, wavelength offsets of 30 nm, 40 nm and 50 nm between the coupled light and the PL peak wavelength of the EAM MQWs are used. The length of the EAMs is 150 μm. The measured dc ER results are shown in Fig.1. The light extinction efficiency of the EAM having low Zn concentration in the InP cladding layer is notably better than the EAM with high Zn doping. For the 40 nm wavelength offset, the ER of the EAM with high Zn doping is 11.1 dB at -5 V. In contrast, the ER of the device having low Zn doping is 18.7 dB at -5 V, which is improved for over 50 %. To the light p-doping, the series resistance is less than 7Ω with the length of 150μm EAM.
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Fig. 1 Extinction ratio versus reverse bias voltage for different wavelength offset of type 1 and type 2
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The Zn atom concentration as a function of material depth of type 1 and type 2 EAMs is measured by SIMS. As is shown in Fig.2, due to diffusion, the Zn concentration in the MQW layer for EAM device having high Zn doping level in the cladding layer is in the range of 1017~1018 cm-3. For the EAM lightly doped cladding layer, however, the Zn concentration in the MQW layer is as low as 1016 cm-3.
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Fig. 2 The zinc atom concentration as a function of material depth
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A 3D EAM model was built with PICS3D Crosslight software, according to device structure shown in Table 1 and the SIMS data as shown in Fig.2. The distribution of electric field in the absorption layer for type 1 and 2 EAMs was calculated respectively. The results of the EAMs at 0V bias are shown in Fig.3.
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Fig. 3 The distribution of the electric field for EAMs of high Zn doping and low Zn doping at 0V
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Though the distribution of electric field in both the devices was not uniform, the fluctuation of the electric field in type 1 EAM is more pronounce than in type 2 device, the amount of which are 1.6×104V/cm and 0.3×104V/cm, respectively. The more uniform electric field distribution can be attributed to the lower Zn concentration in the MQWs layer.
4. Simulation and Optimization of EAMs
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To reduce the working bias voltage of EAMs, we need the increase of not only the ER but also the extinction efficiency. Normally, well thickness of MQWs should be increased to enhance the absorption coefficient per unit length. To study the effects of well thickness, we increase the well thickness by 30% to 6.5 nm, and decrease the thickness of SCH layer to 95.5 nm in order to keep the same active layer thickness as type 2 device. The length of the EAMs is 150 μm. By the 3D EAM simulation, we calculated the extinction characteristics of the EAMs with wavelength offsets of 30 nm, 40 nm and 50 nm between the incident light and the PL peak wavelength of the EAM MQWs. Fig.4 shows the simulated ER of the EAMs with 6.5 nm and 5 nm well thickness and different wavelength offsets. We can see that the simulated EAMs have large ER in a wide wavelength offset range. What is more, at a given voltage and before saturation, the ER of the EAM with 6.5 nm well is notably larger than the EAM with 5 nm well thickness.
Fig. 4 The simulated extinction ratio of the EAMs with 6.5 nm and 5 nm well thickness and different wavelength offsets.
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To verify the well thickness dependence of the ER, type 3 EAM samples were fabricated. The MQWs of the device consist 5 quantum wells and 6 barriers. The thickness of well and SCH layers were 6.5 nm and 95.5 nm respectively. The fabrication process was same as type 2 EAM. The length of the EAM is also 150 μm. The extinction characteristics of the EAMs with different wavelength offsets are shown in Fig.5. As can be seen, the variation trends of the measured ER agree well with the simulations. At a given bias voltage, a smaller wavelength offset leads to a larger ER. What is more, the ER of the EAM with 5 nm well (type 2) is clearly smaller than the EAM with 6.5 nm well thickness at a given reverse bias voltage. Both the simulation and experimental results show that a large well thickness helps to enhance the performance of EAMs. The optical ER and extinction efficiency of the optimized EAM is comparable with those of the EAMs reported in earlier references [1,6].
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Fig. 5 The extinction characteristics of EAMs with different well thickness and wavelength offset for type 3 and type 2.
5. Conclusion
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In conclusion, the ER of EAM device is influenced by the uniformity of electric field in the EAM absorption layer, and the uniformity of electric field in the EAM absorption layer is severely affected by the concentration of Zn diffusing into absorption layer. Therefore, decreasing the concentration of Zn diffusing into the absorption layer is effective to improve the ER of EAM device. In addition, the extinction efficiency of EAMs is improved in the minor well thickness changes by the simulation and optimization, which can make EAMs satisfy extinction requirement for integrating with MQWs lasers. With optimized EAM designs, we have obtained an EAM with the ER over 20 dB at a low bias voltage. The extinction efficiency of the optimized EAM is twice as high as that of the device fabricated by selective area growth technology [5], and which can satisfy commercial application requirements [1-3].
Acknowledgments
A
The work is supported by National Key Research and Development Program of China 2017YFF0206103, National Natural Science Foundation of China ( 61320106013, 61635010, 61474112, 61574137, 61504170).
References [1] T. Ido, H. Sano, D. J. Moss, S. Tanaka and A. Takai, Strained InGaAs/InAlAs MQW Electro-Absorption Modulators with Large Bandwidth and Low Driving Voltage, IEEE Photon. Technol. Lett. 6 (1994) 1207-1209. [2] M. Matsuda, K. Morito, K. Yamaji, T. Fujii and Y. Kotaki, A novel method for designing chirp characteristics in electroabsorption MQW optical modulators, IEEE Photon. Technol. Lett. 10 (1998) 364-366. [3] H. Fukano, T. Yamanaka and M. Tamura, Design and fabrication of low-driving-voltage electroabsorption modulators
5
A
CC E
PT
ED
M
A
N
U
SC RI PT
operating at 40 Gb/s, J. Light. Technol. 25 (2007) 1961-1969. [4] L. S. Han, S. Liang, H. T. Wang, L. J. Qiao, J. J. Xu, L. J. Zhao, H. L. Zhu, B. J. Wang and W. Wang, Electroabsorption-modulated widely tunable DBR laser transmitter for WDM-PONs, Opt. Express, 22 (2014) 30368-30376. [5] D. B. Zhou, H. T. Wang, R. K. Zhang, B. J. Wang, B. Jing, X. An, D. Lu, L. J. Zhao, H. Z. Zhu, C. Ji and W. Wang, Fabrication of 32 Gb/s Electroabsorption Modulated Distributed Feedback Lasers by Selective Area Growth Technology, Chin. Phys. Lett. 32 (2015) 054205-1-3. [6] M. K. Chin and W. S. C. Chang, Theoretical Design Optimization of Multiple-quantum-well electroabsorption waveguide modulators, IEEE J. Quantum Electron. 29 (1993) 2476-2488. [7] M. Aoki, M. Suzuki, H. Sano, T. Kawano, T. Ido, T. Taniwatari, K. Uomi and A. Takai, InGaAdInGaAsP MQW Electroabsorption Modulator Integrated with a DFB Laser Fabricated by Band-Gap Energy Control Selective Area MOCVD, J. Quantum Electron. 29 (1993) 2088-2096. [8] C. Zhang, H. L. Zhu, S. Liang, X. Cui, H. T. Wang, L. J. Zhao and W. Wang, Ten-channel InP-based large-scale photonic integrated transmitter fabricated by SAG technology, Opt. Laser Technol. 64 (2014) 17-22. [9] D. B. Zhou, R. K. Zhang, H. T. Wang, B. J. Wang, J. Bian, X. An, L. J. Zhao, H. L. Zhu, C. Ji and W. Wei, The Effect of Zinc Diffusion on Extinction Ratio of MQW Electroabsorption Modulator Integrated with DFB Laser, in: SPIE/COS Photonics Asia, Beijing, China, 2015, pp. 926714-1-6. [10] S. Wang, Principles of distributed feedback and distributed Bragg-reflector lasers, IEEE J. Quantum Electron. 10(1974) 413-427. [11] K. Kadoiwa, K. Ono and Y. Ohkura, Zn diffusion behavior at the InGaAsP/InP heterointerface grown using MOCVD, J. Cryst. Growth 297 (2006) 44-51. [12] C. L. Reynolds, V. Swaminathan, M. Geva, L. E. Smith and L. C. Luther, Unintentional zinc diffusion in inp pn-homojunctions, J. Electron. Mater. 24 (1995) 747-750. [13] Y. Kawashima, T. Ide and K. Shimizu, Backside SIMS analysis of zinc properties in InGaAsP, J. Surf. Anal. 5 (1999) 116-119. [14] K. Kurishima, T. Kobayashi and H. Ito, Control of Zn diffusion in InP/InGaAs heterojunction bipolar transistor structures grown by metalorganic vapor phase epitaxy, J. Appl. Phys. 79 (1996) 4017-4023.
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S0030-4026(19)30128-7 https://doi.org/10.1016/j.ijleo.2019.02.011 IJLEO 62338
To appear in: Received date: Revised date: Accepted date:
22 June 2018 21 December 2018 2 February 2019
Please cite this article as: Zhou D-bing, Liang S, Wang H-tao, Zhao W, Zhang R-kang, Zhao L-juan, Wang W, Analysis and Optimization of 1.5-m InGaAsP/InP MQWs electroabsorption modulator, Optik (2019), https://doi.org/10.1016/j.ijleo.2019.02.011 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Analysis and Optimization of 1.5-μm InGaAsP/InP MQWs electroabsorption modulator Dai-bing Zhou*, Song Liang, Hui-tao Wang, Wu Zhao, Rui-kang Zhang, Ling-juan Zhao, Wei Wang Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Science,
SC RI PT
College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, Beijing 100083, China.
Abstract: The effects of doping profile and well thickness on the light extinction properties of electroabsorption modulators (EAM) are studied experimentally. It is found that both light p type doping in the InP cladding layer and a large well thickness help to get higher extinction ratios at a given reverse bias voltage. A 3D EAM model has been built for optimizing the performance of EAMs. The simulation results are in a good agreement with the experimental results. With the optimized EAM designs, a modulator with an over 20 dB extinction ratio at a low bias voltage is demonstrated.
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Keywords: Electroabsorption modulator (EAM), Multiple quantum well (MQW), Extinction ratio.
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1. Introduction
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ED
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EAMs based on the Quantum Confined Stark Effect (QCSE) have been used in the optical fiber communication systems as important components, due to their low cost, compact size and easy integration with other devices [1-5]. To obtain a high absorption coefficient, EAM is normally designed to have quantum wells, which have larger thickness than barriers to achieve large extinction ratio (ER) under a low bias voltage [6,7]. But this cannot be realized when EAM is integrated with lasers by the selective area growth or identical active layer technology [8,9], in which both the EAM and laser multiple quantum wells (MQWs) are grown in the same epitaxy run. Different from EAMs, MQWs with thin wells are needed to obtain high performance lasers [10]. Normally, the p type dopant in the cladding layer of EAMs is Zn, which diffuses into the MQWs during the cladding layer growth, weakening the quantum confined Stark effect, and in turn deteriorating the EAM performance. Thus, the doping level in the cladding layer should be optimized to reduce the Zn diffusion while maintaining a low device resistance. In this work, we build a 3D EAM model to analyze the effects of Zn diffusion and well thickness of MQWs on the performance of EAMs [11-14]. The aim of this study is to analyze and optimize the performance of EAM by adjusting only a few parameters, making the performance of the EAMs suitable for application requirements. Several different types of EAM devices are fabricated by adjusting the p-type Zn doping distribution, which is measured by Secondary ion mass spectrometer (SIMS). By running the model with the measured Zn distribution, it is shown that the distribution of electric field in the active region is changed by the Zn diffusion into separate confinement heterostructure (SCH) layer, thus the quantum confined Stark effects is weakened. Then, we simulate and optimize the optical extinction efficiency of EAMs by changing the well thickness of MQWs. Optical transmission characteristics of the fabricated EAMs are in good agreement with the simulations. The ER performance of the EAM is enhanced and the driving voltage is reduced with a large well thickness.
2. Device Design and Fabrication In this study, the EAMs are designed into the three different types of structures. Type 1 EAM has the same MQW structure as type 2, but type 1 has higher p-type Zn doping concentrations than type 2 EAM. The p-type Zn doping
1
Thickness of type 1 and type 2 (nm)
Layer
Thickness of type 3 (nm)
Substrate
SC RI PT
concentration of type 3 is the same as type 2, but the quantum well thickness is increased by 30% compared to type 2, and the thickness of the SCH layer is decreased to 95.5 nm in order to have the same total thickness of the active layer. The three types of EAMs have the same fabrication process. The epitaxial layer structure of EAM is shown in Table 1. The EAMs were fabricated by the following procedures. First, an 800 nm InP buffer layer was grown on an n-type Si-doped InP substrate by metal organic chemical vapor deposition (MOCVD). Then, multiple quantum wells which consist six InGaAsP wells and seven InGaAsP barrier layers were grown, which were sandwiched between two InGaAsP SCH layers. The 20 oC photoluminescence (PL) wavelength of the MQWs is 1500 nm. Finally, a p-type InP cladding layer and InGaAs contact layer were grown. A 3-μm-wide ridge waveguide was formed by wet etching technology. Then, Ti/Au p-electrode was sputtered and patterned on the p-side of the device. After thinning the wafer to about 150 μm, Au/Ge/Ni n-electrode was deposited. The obtained EAMs are mounted on AlN heat sinks for measurements. Table 1．Epitaxial Material Structure Material
PL wavelength (nm)
n-InP n-InP
920
Lower SCH
100
95.5
i-InGaAsP
1200
Well
5
6.5
i-InGaAsP
1500
Barrier
10
10
i-InGaAsP
1200
Upper SCH
100
95.5
i-InGaAsP
1200
Cladding layer
1500
1500
p-InP
920
Contact layer
300
300
p-InGaAs
U
800
N
800
M
A
Buffer layer
ED
3. Effects of Zn Diffusion on Modulation Performance
A
CC E
PT
A tunable laser was used as a light source during the dc ER tests. TE polarized lights with different wavelengths were coupled into and out of the EA modulators by tapered single-mode fibers. The coupling efficiency between the chip and the single-mode fiber is 45%. In this study, wavelength offsets of 30 nm, 40 nm and 50 nm between the coupled light and the PL peak wavelength of the EAM MQWs are used. The length of the EAMs is 150 μm. The measured dc ER results are shown in Fig.1. The light extinction efficiency of the EAM having low Zn concentration in the InP cladding layer is notably better than the EAM with high Zn doping. For the 40 nm wavelength offset, the ER of the EAM with high Zn doping is 11.1 dB at -5 V. In contrast, the ER of the device having low Zn doping is 18.7 dB at -5 V, which is improved for over 50 %. To the light p-doping, the series resistance is less than 7Ω with the length of 150μm EAM.
2
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Fig. 1 Extinction ratio versus reverse bias voltage for different wavelength offset of type 1 and type 2
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ED
M
A
N
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The Zn atom concentration as a function of material depth of type 1 and type 2 EAMs is measured by SIMS. As is shown in Fig.2, due to diffusion, the Zn concentration in the MQW layer for EAM device having high Zn doping level in the cladding layer is in the range of 1017~1018 cm-3. For the EAM lightly doped cladding layer, however, the Zn concentration in the MQW layer is as low as 1016 cm-3.
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Fig. 2 The zinc atom concentration as a function of material depth
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A 3D EAM model was built with PICS3D Crosslight software, according to device structure shown in Table 1 and the SIMS data as shown in Fig.2. The distribution of electric field in the absorption layer for type 1 and 2 EAMs was calculated respectively. The results of the EAMs at 0V bias are shown in Fig.3.
3
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Fig. 3 The distribution of the electric field for EAMs of high Zn doping and low Zn doping at 0V
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Though the distribution of electric field in both the devices was not uniform, the fluctuation of the electric field in type 1 EAM is more pronounce than in type 2 device, the amount of which are 1.6×104V/cm and 0.3×104V/cm, respectively. The more uniform electric field distribution can be attributed to the lower Zn concentration in the MQWs layer.
4. Simulation and Optimization of EAMs
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PT
ED
M
A
To reduce the working bias voltage of EAMs, we need the increase of not only the ER but also the extinction efficiency. Normally, well thickness of MQWs should be increased to enhance the absorption coefficient per unit length. To study the effects of well thickness, we increase the well thickness by 30% to 6.5 nm, and decrease the thickness of SCH layer to 95.5 nm in order to keep the same active layer thickness as type 2 device. The length of the EAMs is 150 μm. By the 3D EAM simulation, we calculated the extinction characteristics of the EAMs with wavelength offsets of 30 nm, 40 nm and 50 nm between the incident light and the PL peak wavelength of the EAM MQWs. Fig.4 shows the simulated ER of the EAMs with 6.5 nm and 5 nm well thickness and different wavelength offsets. We can see that the simulated EAMs have large ER in a wide wavelength offset range. What is more, at a given voltage and before saturation, the ER of the EAM with 6.5 nm well is notably larger than the EAM with 5 nm well thickness.
Fig. 4 The simulated extinction ratio of the EAMs with 6.5 nm and 5 nm well thickness and different wavelength offsets.
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To verify the well thickness dependence of the ER, type 3 EAM samples were fabricated. The MQWs of the device consist 5 quantum wells and 6 barriers. The thickness of well and SCH layers were 6.5 nm and 95.5 nm respectively. The fabrication process was same as type 2 EAM. The length of the EAM is also 150 μm. The extinction characteristics of the EAMs with different wavelength offsets are shown in Fig.5. As can be seen, the variation trends of the measured ER agree well with the simulations. At a given bias voltage, a smaller wavelength offset leads to a larger ER. What is more, the ER of the EAM with 5 nm well (type 2) is clearly smaller than the EAM with 6.5 nm well thickness at a given reverse bias voltage. Both the simulation and experimental results show that a large well thickness helps to enhance the performance of EAMs. The optical ER and extinction efficiency of the optimized EAM is comparable with those of the EAMs reported in earlier references [1,6].
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Fig. 5 The extinction characteristics of EAMs with different well thickness and wavelength offset for type 3 and type 2.
5. Conclusion
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PT
ED
In conclusion, the ER of EAM device is influenced by the uniformity of electric field in the EAM absorption layer, and the uniformity of electric field in the EAM absorption layer is severely affected by the concentration of Zn diffusing into absorption layer. Therefore, decreasing the concentration of Zn diffusing into the absorption layer is effective to improve the ER of EAM device. In addition, the extinction efficiency of EAMs is improved in the minor well thickness changes by the simulation and optimization, which can make EAMs satisfy extinction requirement for integrating with MQWs lasers. With optimized EAM designs, we have obtained an EAM with the ER over 20 dB at a low bias voltage. The extinction efficiency of the optimized EAM is twice as high as that of the device fabricated by selective area growth technology [5], and which can satisfy commercial application requirements [1-3].
Acknowledgments
A
The work is supported by National Key Research and Development Program of China 2017YFF0206103, National Natural Science Foundation of China ( 61320106013, 61635010, 61474112, 61574137, 61504170).
References [1] T. Ido, H. Sano, D. J. Moss, S. Tanaka and A. Takai, Strained InGaAs/InAlAs MQW Electro-Absorption Modulators with Large Bandwidth and Low Driving Voltage, IEEE Photon. Technol. Lett. 6 (1994) 1207-1209. [2] M. Matsuda, K. Morito, K. Yamaji, T. Fujii and Y. Kotaki, A novel method for designing chirp characteristics in electroabsorption MQW optical modulators, IEEE Photon. Technol. Lett. 10 (1998) 364-366. [3] H. Fukano, T. Yamanaka and M. Tamura, Design and fabrication of low-driving-voltage electroabsorption modulators
5
A
CC E
PT
ED
M
A
N
U
SC RI PT
operating at 40 Gb/s, J. Light. Technol. 25 (2007) 1961-1969. [4] L. S. Han, S. Liang, H. T. Wang, L. J. Qiao, J. J. Xu, L. J. Zhao, H. L. Zhu, B. J. Wang and W. Wang, Electroabsorption-modulated widely tunable DBR laser transmitter for WDM-PONs, Opt. Express, 22 (2014) 30368-30376. [5] D. B. Zhou, H. T. Wang, R. K. Zhang, B. J. Wang, B. Jing, X. An, D. Lu, L. J. Zhao, H. Z. Zhu, C. Ji and W. Wang, Fabrication of 32 Gb/s Electroabsorption Modulated Distributed Feedback Lasers by Selective Area Growth Technology, Chin. Phys. Lett. 32 (2015) 054205-1-3. [6] M. K. Chin and W. S. C. Chang, Theoretical Design Optimization of Multiple-quantum-well electroabsorption waveguide modulators, IEEE J. Quantum Electron. 29 (1993) 2476-2488. [7] M. Aoki, M. Suzuki, H. Sano, T. Kawano, T. Ido, T. Taniwatari, K. Uomi and A. Takai, InGaAdInGaAsP MQW Electroabsorption Modulator Integrated with a DFB Laser Fabricated by Band-Gap Energy Control Selective Area MOCVD, J. Quantum Electron. 29 (1993) 2088-2096. [8] C. Zhang, H. L. Zhu, S. Liang, X. Cui, H. T. Wang, L. J. Zhao and W. Wang, Ten-channel InP-based large-scale photonic integrated transmitter fabricated by SAG technology, Opt. Laser Technol. 64 (2014) 17-22. [9] D. B. Zhou, R. K. Zhang, H. T. Wang, B. J. Wang, J. Bian, X. An, L. J. Zhao, H. L. Zhu, C. Ji and W. Wei, The Effect of Zinc Diffusion on Extinction Ratio of MQW Electroabsorption Modulator Integrated with DFB Laser, in: SPIE/COS Photonics Asia, Beijing, China, 2015, pp. 926714-1-6. [10] S. Wang, Principles of distributed feedback and distributed Bragg-reflector lasers, IEEE J. Quantum Electron. 10(1974) 413-427. [11] K. Kadoiwa, K. Ono and Y. Ohkura, Zn diffusion behavior at the InGaAsP/InP heterointerface grown using MOCVD, J. Cryst. Growth 297 (2006) 44-51. [12] C. L. Reynolds, V. Swaminathan, M. Geva, L. E. Smith and L. C. Luther, Unintentional zinc diffusion in inp pn-homojunctions, J. Electron. Mater. 24 (1995) 747-750. [13] Y. Kawashima, T. Ide and K. Shimizu, Backside SIMS analysis of zinc properties in InGaAsP, J. Surf. Anal. 5 (1999) 116-119. [14] K. Kurishima, T. Kobayashi and H. Ito, Control of Zn diffusion in InP/InGaAs heterojunction bipolar transistor structures grown by metalorganic vapor phase epitaxy, J. Appl. Phys. 79 (1996) 4017-4023.
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