The influences of contact electrode shape and vertical illumination direction on the performance of p-i-n photodiodes (PDs) are studied by theory and experiment. The PDs with ring-covered p-contact electrode (RCC-PD) and fully-covered p-contact electrode (FCC-PD) were fabricated and tested. For the RCC-PD, the influences of p-side and n-side illumination on the bandwidth also analysed. The results show that for the PDs with 40 mu m mesa diameter under -3 V bias and 7.0 mA output photocurrent, a 40.6 and 31.6% increase of bandwidth and responsivity in the FCC-PD compared with RCC-PD. The 3 dB bandwidth and responsivity of the FCC-PD with a 40 mu m mesa diameter at -3 V bias can reach 33.6 GHz and 0.5 A/W, respectively.

In this paper, we propose a monolithic integration of vertical-cavity surface-emitting laser (VCSEL) and coupled cavity resonant cavity enhancement photodiode (ccRCEPD). Based on this structure, a couple of matched chips is designed for single fiber bidirectional optical interconnects. That type of integration can easily put VCSEL and (photodiode) PD into one package, which not only reduces the costs of the device packages and even cut the costs of the optical system like beam splitter, but also can save the space in optical transceiver to make it tight. These chips’ VCSELs show a threshold current of 1.6 mA and 1.7 mA, and a slope efficiency of 0.74 W/A and 0.97 W/A. VCSELs’ modulation bandwidth is 9.5 GHz and 11.0 GHz, and PDs’ response bandwidth is 10 GHz. Furthermore, the modulation bandwidth can be higher if the material of the multiple quantum wells (MQWs) is transformed GaAs/AlGaAs to InGaAs/AlGaAs. And by optimizing, the 3dB bandwidth of PD will be higher.

In this paper, the performance of uni-traveling carrier photodetector is investigated operating back, front and double light illuminating ways. The simulation results show that the back illuminated device shows the best performance. And the 3-dB bandwidth and responsivity are 26 GHz and 0.179 A/W, respectively. The front illuminated device shows the highest saturation characteristics, reaching to 1.9e5 W/cm2. The active layer radius of device is 14 μm and reverse bias is 0.1 V. In addition, the reasons account for the performance difference can be summed up as the following three points:Absorption of light by p-contact layer, the reflection of anode and the differences of electric field profile in the absorption layer.

The fabrication and characterization of p-i-n photodiodes integrated with wide spectrum focusing reflectors using nonperiodic strip and concentric-circular subwavelength gratings are presented. The experimental results show that the gratings can reflect and focus the incident light on the absorber of the photodiode, and thus can simultaneously achieve high speed and high efficiency. For the gratings’ integrated photodiodes, the responsivity is improved over a wide spectral range, and when the absorber was 600 nm and the mesa diameter was 40 μm, a responsivity of 0.46 A/W at a wavelength of 1.55 μm and a 3 dB bandwidth of 21.6 GHz under a reverse bias of 3 V were simultaneously obtained. OCIS codes: 130.3120, 230.5170, 250.0040. doi: 10.3788/COL201816.051301.

In this paper, the bias-free operational uni-traveling-carrier photodiode (UTC-PD) for terahertz wave generation is designed via physics-based simulation. The physics-based model is established at first and then the reliability of the simulation is demonstrated by comparison to previously reported experimental results. The epitaxial layers of the UTC-PD are analyzed and investigated to improve its bandwidth and output-power simultaneously. By optimizing the spacers and the collector, and using a combination of optimal graded-doping profile and graded-bandgap material for the absorber, the 3-dB bandwidth and the peaked output-power of the UTC-PD are improved by 36.5% and 2.262 dB, respectively. The 3-dB bandwidth of the optimized bias-free operational UTC-PD with mesa diameter of 8, 6, 5, 4 and 3-μm can achieve 106, 137.67, 158.3, 183 and 211 GHz, respectively.

In this paper, the high-speed modified uni-traveling-carrier photodiode (MUTC-PD) was designed and fabricatedfor low reverse bias. The 3-dB bandwidth and responsivity of MUTC-PD with 24-μm mesa diameter at 1-V reverse bias is 22.5 GHz and 0.22 A/W at the wavelength of1550 nm, respectively. The dark current of the device is less than 4nA at 3.3 V reverse bias. The fabricated device can achieve high performance at low reverse bias is confirmed.

With the development of optical communication system, the nonlinear saturation characteristics of photodetectors are necessary to consider. We observed the 1-dB compression current as DC photocurrent saturation point under high power illumination in PIN-PDs. Meanwhile, a new method of measuring AC saturated output power in the time domain is proposed. The quantitative relationship between DC saturation point and AC saturation point is given.

A vertically integrated device composed of Vertical-Cavity Surface-Emitting Laser (VCSEL) unit and Resonant Cavity Enhanced Photodiode (RCE-PD) unit is proposed, which has huge potential application perspectives for optical interconnects. The performance of the integrated device and the interaction of its two composing units are analyzed based on different structure optimization. As optimized, its two units can be functionally decoupled from each other. For VCSEL unit, the threshold current is 1.25 mA and the slope efficiency is 0.89W/A. For RCE-PD unit, the quantum efficiency is up to 90.5%.

We present a two-element back-illuminated symmetric-connected uni-traveling-carrier photodiode array (SC-PDA) integrated with sub-wavelength-gratings based beam-splitter (SWGs-BS) for high power optoelectronic applications. The SC-PDA with SWGs-BS, a top-illuminated SC-PDA and a single PD were fabricated and tested. The proposed SC-PDA with SWGs-BS demonstrates a 3dB bandwidth of 23.8GHz@60mA, a saturation current of 87.9mA@12GHz and a maximum output RF power of ~16dBm@12GHz. Compared to the top-illuminated SC-PDA and the single PD, the proposed SC-PDA with SWGs-BS achieved high-power handling capability at low coupling complexity and requires no phase-matching techniques in the system.

We designed and optimized a high-speed, low-loss electrodes applied to photodiode array (PDA) using simulating software HFSS. Optimized and un-optimized electrodes were fabricated and tested. A 1.1dB reduce of the insertion loss at 40GHz was achieved by the optimization. Meanwhile, photodiode array implementing the optimized electrodes has a 6.6GHz higher 3dB-bandwidth comparing to the photodiode with un-optimized electrodes.

Two measurement techniques are investigated to characterize photodetector linearity. A model for the two-tone and three-tone photodetector systems is developed to thoroughly investigate the influences of setup components on the measurement results. We demonstrate that small bias shifts from the quadrature point of the modulator will induce deviation into measurement results of the two-tone system, and the simulation results correspond well to experimental and calculation results.

A VCSEL and a Resonant Cavity Enhancement Photodiode are vertically integrated and can be functionally optical decoupled and electrical isolation. The threshold current of VCSEL is 1.67 mA, and FWHM of RCE-PD is 13 nm.

The subwavelength grating structure was fabricated by inductively coupled plasma etching (ICP) in a mixture of Cl2/Ar/O2 on semi-insulating GaAs (100) substrate.The impact of the etching conditions,including but not limited to the compositions and flow-rates of Cl2,Ar and O2mixture,aperture size,pressure,etching time and temperature,on the etching rate and surface morphologies was investigated with atomic force microscopy.The results show that the flow-rates and compositions of Cl2,Ar and O2,andetchingaperture sizeall have a major impact on the etching-rate and surface roughness.To be specific,at the fixed Cl2/Ar/O2 compositions,as the total flow-rate increased,the etching-rate increased;the etching aperture size and Cl2 flow-rate affected the etching-rate to varying degrees.ICP etching little affected the GaAs surface roughness,simply because of ～5 ％ oxygen.Possible ICP etching mechanisms were tentatively discussed.

We demonstrate a two-element symmetric-connected photodiode array (SC-PDA) for high-power and high-speed applications. A traditional traveling-wave photodiode array (TW-PDA), an SC-PDA, and a single PD with the same epitaxial structure were fabricated and tested. Both the TW-PDA and SC-PDA have higher saturation currents, larger RF power, and better high-power and high-frequency responses than the single PD. However, the results show that the SC-PDA has a higher responsivity (0.32 A/W), a smooth frequency response (14.0 GHz), and a higher saturation current (66 mA) than the TW-PDA (0.24 A/W, periodically patterned frequency response and 42 mA) without using phase matching techniques.

A novel uni-traveling-carrier photodetector (UTC-PD), bonded to high-reflectivity (HR) distributed Bragg reflector (DBR) mirrors, referred to as HR-UTC-PD, is first developed to overcome the bandwidth-responsivity tradeoff in UTC-PDs at various wavelengths. Grubbs' test is adopted, for the first time, to measure the bonded thickness of random locations for evaluating the reflected light loss generated in the bonded region. Compared with a standard UTC-PD without HR DBR mirrors, the maximum improvement of HR-UTC-PD responsivity (0.88A/W at 1560 nm) is 24.4% under a bias voltage of 3 V. The obtained 3-dB bandwidth for a 40-mu m-diameter PD, which is neither increased nor degraded with the HR DBR mirrors, is 13.87 GHz at a bias voltage of 6 V and a 1550 nm wavelength. The saturation current up to 50 mA at 1-dB compression point is obtained at the frequency of 10 GHz, under a 50-Omega load and a 6 V bias voltage.

By introducing p + -InAlAs layer and InGaAsP intrinsic layer, an InP-based p-i-n photodetector with wide spectral range and low dark current is fabricated. The responsivity is 0.45A/W and 0.41A/W respectively at 850nm and 1550nm wavelengths.

We propose a universal simulating solution to characterize the OIP3 of most kinds of photodetectors using Silvaco TCAD simulation tools. For a normal PIN photodetector and a unitraveling-carrier photodetector, a fine agreement was observed in experimental results and simulation results. We believe that this solution could be useful in designing and optimizing high-power photodetectors.

A polarization-insensitive 2D high index contrast gratings (HCGs) beam splitter based on silicon-on-insulator(SOI) is proposed and demonstrated, which performs two independent functions: transmission focusing and power equalization at the wavelength of 1550 nm.

In this paper, the reliability of transient simulation results of uni-traveling-carrier photodiodes (UTC-PDs) is demonstrated by compared with experimental and reported simulation results, when the parameters of drift-diffusion model are set correctly.

The 3dB-bandwidth versus incident optical intensity and saturation property of modified uni-traveling carrier photodiode (MUTC-PD) was simulated. When the optical intensity is less than 5.13 x10(5)W/cm(2), the MUTC-PD could maintain linear output power and its bandwidth could reach 134.8GHz at 0V.