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.

A planar InGaAs/InAlAs single photon avalanche diode (SPAD) was fabricated and comprehensively characterized. At room temperature, the dark count rate is 3.1 MHz at 10.4% photon detection efficiency. The corresponding noise-equivalent power of 3.07 × 10 ⁻¹⁵ W/Hz ^1/2 is achieved, which is the lowest value among reported InGaAs/InAlAs SPADs operated at room temperature. Moreover, it is the first time to report an InGaAs/InAlAs SPAD driven by a sine wave gate (SWG) quenching circuit as a receiver in the photon counting communication system. For achieving high-bit-rate transmission with high sensitivity, a high-frequency (1.8 GHz) SWG quenching circuit is developed and the time jitter for the system is reduced to 53 ps. At bit rates of 100 Mbit/s, 200 Mbit/s, and 400 Mbit/s, the sensitivities of −57.2 dBm, −53.42 dBm, and −51.06 dBm are experimentally demonstrated with a single InGaAs/InAlAs SPAD respectively. In addition, a theoretical sensitivity of −42.7 dBm is predicted at 1.8 Gbit/s with a 4 × 4 InGaAs/InAlAs SPAD array.

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.

With the rapid development of photo-communication technologies, avalanche photodiode (APD) will play an increasingly important role in the future due to its high quantum efficiency, low power consumption, and small size. The monolithic integration of optical components and signal processing electronics on silicon substrate chips is crucial to driving cost reduction and performance improvement; thus, the technical research on InGaAs/Si APD is of great significance. This work is the first to demonstrate the use of a photon-trapping (PT) structure to improve the performance of the InGaAs/Si APD based on an SOI substrate, which exhibits very high absorption efficiency at 1310 nm wavelength while the thickness of the absorption layer is kept at 800 nm. Based on the optical and electrical simulations, an optimized InGaAs/Si PT-APD is proposed, which exhibits a better performance and a higher responsivity compared to the original InGaAs/Si APD.

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 aa_b⁰-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.