A top-illuminated planar InAlAs/InGaAs Avalanche Photodiode (APD) with Separation Absorption, Charge and Multiplication (SACM) structure has been demonstrated. The fabricated APD results showed that the maximum 3dB bandwidth of the APD reaches 33 GHz at M=2. The dark current is 1 μA at 0.9 breakdown voltage, and the unit responsivity is 0.3 A/W operating at 1.55 μm. The maximum gain of the device is 20, when the incident light intensity is 20 μW. It is important to emphasize that the active area diameter of the fabricated device is 15 μm. Such a large active area diameter provides greater alignment tolerance for fiber coupling compared to using waveguide structures. These characteristics demonstrate the potential of planar InAlAs/InGaAs -APDs for 50-Gbit/s Passive Optical Networks (PONs) in optical communication systems.
With the rise of cloud computing, big data, and mobile internet, there is an increasing demand in information society for higher communication bandwidth and speed. There is an urgent need to conduct research on the next generation of ultra-high-speed transmission networks, with high-speed photodetectors being key components. We designed and fabricated a high responsivity, high bandwidth, and high output power edge-coupled Uni-Traveling Carrier Photodetector (UTC-PD). This paper details the structural design, experimental fabrication, and test results of a 1550nm wavelength InP-based edge-coupled UTC-PD. To achieve high responsivity and bandwidth simultaneously, we optimized the thickness of the absorption and collection layers. The device was fabricated using metal organic chemical vapor deposition and contact lithography techniques. The test results show that at a wavelength of 1550nm, the UTC-PD achieves a photoresponse of 0.49A/W (without anti-reflection coating). We conducted high-frequency performance testing of the photodetector using a vector network analyzer. Photodetectors of the same size exhibited uniform bandwidth performance, with a maximum bandwidth reaching up to 34.1GHz. At an optical current of 2.85mA, the photodetector exhibits RF output powers of 247uW @ 1GHz and 26.8uW @ 91GHz, with a reduction of 8.96dB within the 90GHz frequency range. This high responsivity, high bandwidth, and high output power photodetector could offer promising chip options for upcoming ultra-high-speed optical transmission networks.
We demonstrate a low current and high bandwidth waveguide photodetector by selective area growth technique. The waveguide photodiode has been fully fabricated by a photonic integration process. The photodiode epitaxial structure is selectively regrown on wafer with SiO2-masked SOA mesas. Before SAG of photodetector layers, SOA mesas are etched into non-reentrant configuration. The SAG process is carried out in low-pressure MOCVD reactor at a high growth temperature of 680 °≅ and growth rate of 5Å/𝑠. Combination of low-speed Ar/Cl2/CH4 dry etching and wet etching is used to define PD mesas. PD mesas are arranged <300μm away from SOA mesa to minimize the growth rate enhancement of SAG. The photodetector is evanescently coupled with a 2μm wide rib waveguide defined by ICP etching. The PD is passivated with 600nm SiO2 by PECVD. The fabricated waveguide photodiode exhibits a dark current of 242pA at -3V, fiber-to-chip responsivity up to 0.18A/W and 3dB electrical bandwidth of 20GHz. The performance shows hardly no compromise when comparing to that of normal discrete devices. Those results lay good foundations for high-function photonic integration circuits in near future.
A parallel array with 8 high speed surface-illuminated pin photodetectors (PDs) is designed and fabricated. The effect of absorption layer thickness on PD responsivity and bandwidth is analyzed, and the material structure is optimized accordingly. The photodetector array, which is based on the Indium Phosphorus (InP) Platform, is manufactured by Metalorganic Chemical Vapor Deposition (MOCVD) and contact photolithography. Each detector has a photosensitive surface diameter of 20μm and a depletion layer thickness of 1.0μm. All 8 pin-PDs exhibit a uniform responsivity over 0.7A/W at 1310nm and a low dark current of below 4nA at 1V reverse bias. In addition, the 8 pin-PDs exhibit a uniform -3dB bandwidth of 20GHz. The experimental results agree well with the theoretical values. The photodetector array, which has a cost-effective and simple manufacturing process, could potentially operate at a total transmission rate beyond 200Gbps for fiber optic communication applications and can be integrated with other optoelectronic devices.
We propose a polarization insensitive multimode interference coupler (MMI) design for optical 90° hybrid. The 90° hybrid used in coherent receiver application is based on the Indium Phosphorus (InP) platform, which can realize monolithic integration with detectors. By using the three dimension beam propagation method, a 90° hybrid based on a polarization insensitive MMI has been designed and optimized. We find that there is an ideal interference length for both transverse electric (TE) mode and transverse magnetic (TM) mode in this structure. Using the designed 90° hybrid, we demonstrate the common mode rejection ratios for in-phase channels and quadrature channels better than -20 dB and the phase errors better than ±3° in an ideal interference length range. The phase errors of the I-channel and Q-channel less than ±4° when the interference length is 480μm across the C band (1535-1560 nm).
This paper reports a planar structure InGaAs/InP avalanche photodetector focal plane arrays. Their material structure use separate absorption, grading, charge and multiplication layer. The pixel pitch of 8×8 format detectors is 250 μm. The breakdown voltage (VBD) is typically in the range of 65 to 70 V for most of the devices on the same wafer. The typical dark current at 90% of VBD is 3 nA, dark currents as low as 0.5 nA at 90% of VBD have also been observed for some diodes, corresponding to a dark current density of 1 × 10-5 A/cm2. The photocurrent starts to increase at the "punch-through" voltage Vp of 43 V. The responsivity at 1.55 μm is 0.91 A/W at unity gain and the multiplication layer is estimated to be 1.2 μm. Each device on the same wafer has excellent characteristics and high uniformity through measurement, laying a solid foundation for 3D imaging laser radar systems.
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