Yanli Zhao

InGaAs–InP avalanche photodiodes with dark current limited by generation-recombination

Separate absorption grading charge multiplication avalanche photodiodes (SAGCM APDs) are widely accepted in photon starved optical communication systems due to the presence of large photocurrent gain. In this work, we present a detailed analysis of dark currents of planar-type SAGCM InGaAs-InP APDs with different thicknesses of multiplication layer. The effect of the diffusion process, the generation-recombination process, the tunneling process and the multiplication process on the total leakage current is discussed. A new empirical formula has been established to predict the optimal multiplication layer thickness of SAGCM APDs with dark current limited by generation-recombination at multiplication gain of 8.

Design of plasmonic photodetector with high absorptance and nano-scale active regions.

We propose a novel plasmonic photodetector with high responsivity, utilizing nano-scale active regions. This design can be applied to diverse materials (group III-V or IV materials) and different operation wavelengths covering the O-U bands. The periodic structure utilizing Surface Plasmon Polariton Bloch Waves (SPP-BWs) has low optical power loss. FDTD simulation shows an absorptance of 74.4% which means a responsivity of about 0.74 A/W at 1550 nm. The low capacitance brings low noise, reduced power consumption, and a high electrical bandwidth which is estimated to be 140 GHz. Among the plasmonic PDs with inherent high speeds but low responsivities, our design makes the obvious progress on improving the absorptance.

The Determination of Unity Gain for InGaAs/InP Avalanche Photodiodes With Excess Noise Measurements

We propose a methodology for determining the unity gain of avalanche photodiodes (APDs) with excess noise measurements. Compared with previous reports, the relative intensity noise from the laser can be deduced in our experiments, which alleviates the strict requirements for the light source during measurements. The unity gain of APDs can be determined from the abrupt change in the derivative function of the total noise versus the photocurrent. With the proposed technique, a relative error for gain is of 3.3%. Thus the excess noise can be extracted from the total noise and the <inline-formula> <tex-math notation=LaTeX>

Schottky photodetector with tapered thin metal strip on silicon waveguide

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Enhanced light absorption in waveguide Schottky photodetector integrated with ultrathin metal/silicide stripe

</tex-math></inline-formula> can be derived with a satisfactory accuracy.

Time Domain Analysis of Hole Trapping Effect in Avalanche Photodiode Using Schrödinger’s Equation

We propose a Schottky photodetector with tapered thin metal strip on SOI platform. Schottky photodetector can detect photons below the semiconductor bandgap energy by exploiting the internal photoemission. In the internal photoemission process, the hot carriers generate in the tapered thin metal strip where light absorption occurs, and part of these carriers can be emitted over the Schottky barrier and collected as photocurrent. The small thickness of the tapered metal strip contributes to a high internal quantum efficiency of 11.25%. This metal-semiconductor structure acts as a photonics-plasmonics mode convertor. According to 3D-FDTD simulation, about 95.8% of the incident optical power can be absorbed in the absorption area within 4.5μm at wavelength of 1550 nm. The responsivity is estimated to be 0.135A/W at 1550 nm. This compact design with a low dark current has a minimum detectable power of -23.15 dβm. We argue that this design can promote the progress of all-Si photo-detection in near-infrared communication band.

Low-Noise 3-D Avalanche Photodiodes

We investigate the light absorption enhancement in waveguide Schottky photodetector integrated with ultrathin metal/silicide stripe, which can provide high internal quantum efficiency. By using aab0-quasi-TE hybrid modes for the first time, a high absorptance of 95.6% is achieved in 5 nm thick Au stripe with area of only 0.14 μm2, without using resonance structure. In theory, the responsivity, dark current, and 3dB bandwidth of the corresponding device are 0.146 A/W, 8.03 nA, and 88 GHz, respectively. For most silicides, the quasi-TM mode should be used in this device, and an optimized PtSi device has a responsivity of 0.71 A/W and a dark current of 35.9 μA.

The Effect of Overvoltage and Gate Signal Voltage on Dark Count Rate of Single Photon Detection

In this letter, a discrete matrix algorithm is proposed for hole-trapping effect analysis of avalanche photodiodes (APDs). Different from the previous thermionic emission model for the interface barrier between InGaAsP grading layer and InGaAs absorption layer, our model adds the particle’s volatility into consideration. By analyzing the wave function of fast moving holes with Schrödinger’s equation, the resonant tunneling effect has been discovered, which is closely related with the bias voltage and thickness of the grading layer. The influences of the whole shape of the barrier, including both height and width, on the impulse response have been investigated. Compared with previous simulation results, in our experimental study, the measured data agree better with the results from new model. Finally, to minimize the hole trapping effect for high speed operation of APDs, the optimal designs for InGaAsP grading layers are derived under different biases.

Bandwidth Improvement of Avalanche Photodiode Using Non-uniformly Doped Multiplication Layer

In this paper, we present a new 3-D structure for the InP-based avalanche photodiode, aiming at decreasing the excess noise factor. To the best of our knowledge, it is the first time new device designs based on the recently developed 3-D spatial dead space model in 2014 have been proposed. In addition, we also propose a methodology, i.e., the 2-D planar absorption distribution projection technique, for further optimizing the 3-D model. According to our theoretical simulation results, by combining photonic crystal and selective area doping, the effective k values of InP and In0.52Al0.48As can be reduced to as low as ~0.19 and as ~0.13, respectively. Meanwhile, the optimal thickness of the multiplication region is larger than 0.45 μm, which reduces the tunneling effect. The detailed parameter optimization process, including optics, electronics, and material, is comprehensively presented. The examples in this paper also provide a fresh idea for researchers to foretell and design new photodetectors with the 3-D structure.

A Coherent Receiver Based on SIM for Quantum Communication

We found that the change of overvoltage has more influence than that of the gate signal voltage on DCR. The lower DCR and higher detection efficiency can be achieved by choosing the voltage appropriately.