High-Speed, High-Efficiency, Large-Area p-i-n Photodiode for Application to Optical Interconnects from 0.85 to 1.55 μm Wavelengths

We demonstrate a novel InP-based photodiode structure with large active diameter (55 μm) for > 25 Gbit/s operation at optical wavelengths which range from 0.85 to 1.55 μm. By utilizing the large absorption constant (>3 μm ^-1) of In 0.53Ga 0.47As-based p-type absorption layer at 0.85 μm wavelength excitation, the slow hole transport can be eliminated in our structure and the tradeoff between RC-limited bandwidth and carrier transient time can be greatly released due to the excellent characteristics of electron transport in the intrinsic and thick In 0.53Ga 0.47As layer (~4 μm). Furthermore, in order to minimize the serious surface (absorption) recombination in the top p-type In 0.53Ga 0.47 As absorption layer, an additional p-type In 0.52Al x Ga 0.48-xAs-graded bandgap layer (GBL) is grown above it. Such a GBL cannot only provide uniform photoabsorption profile, but also accelerates the electron diffusion process. Under -1 V bias, these devices can achieve high-speed (14 and 22 GHz), and high responsivity (0.25 and 0.9 A/W), at 0.85 and 1.55 μm wavelength operation, respectively. Clear eye-opening (error-free) with data rate up to around 30 Gbit/s have also been demonstrated at both wavelengths.