Large-Area p-i-n Photodiode With High-Speed and High-Efficiency Across a Wide Optical Operation Window (0.85 to 1.55 μm)

We demonstrate novel InP based photodiodes, which eliminate the degradation in speed and efficiency under short wavelength (0.85 μm) operation and have a enlarged device diameter as compared to that of GaAs based PDs for the same desired speed performance. By inserting a p-type In
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Al
_0.32
Ga
_0.16
As layer with an intermediary bandgap value (1.2 eV) between In
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Al
_0.48
As (1.47 eV) window and In
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Ga
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As (0.75 eV) absorption layers, the huge surface absorption (recombination), which would lead to efficiency degradation, under short wavelength excitation can be diluted. The slow hole transport in our structure can also be diminished due to the p-type doping in these absorption layers. Furthermore, the trade-offs between RC-limited bandwidth (device size) and carrier transient time in GaAs based PDs can be further released due to the excellent electron transport characteristic in the In
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Ga
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As (collector) layer. These devices with a large diameter as 62 μm, which is the usual size of 10 Gbit/s InP based PDs, can achieve wide 3-dB bandwidths; varying from 25 to 17 GHz when the operating wavelengths changes from 0.85 to 1.55 μm. A constant and high external efficiency (~74%) with a clear eye-opening at around 40 Gbit/s has also been achieved over this wide optical window.