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High-frequency behavior of waveguide integrated photodiodes monolithically integrated on InP using optical butt coupling

: Umbach, A.; Leone, A.M.; Unterborsch, G.


Journal of applied physics 81 (1997), No.6, pp.2511-16
ISSN: 0021-8979
ISSN: 1089-7550
Journal Article
Fraunhofer HHI ()
carrier mobility; gallium arsenide; gallium compounds; iii-v semiconductors; indium compounds; integrated optoelectronics; optical waveguides; p-i-n photodiodes; semiconductor growth; vapour phase epitaxial growth; waveguide integrated photodiodes; high-frequency behavior; inp; optical butt coupling; GaInAsP/InP material system; optoelectronical integrated circuits; high-speed detectors; high quantum efficiency; smallest detector sizes; selective embedded growth; metal-organic vapor-phase epitaxy; partially masked substrates; detector bandwidth; quantum efficiency; enhanced diffusion component; 50 GHz; 8 GHz; 4 mum; GaInAsP-InP

p-i-n photodiodes with integrated optical waveguides were successfully fabricated in the GaInAsP/InP material system. This integration leads to optoelectronical integrated circuits of significantly increased functionality, and it also offers the possibility to build high-speed detectors with high quantum efficiency. Butt-joint coupling between waveguide and photodiode was used allowing smallest detector sizes. Selective embedded growth of the photodiode layer stack was accomplished by metal-organic vapor-phase epitaxy on partially masked substrates. This technique was proven to be suitable for device fabrication. To study the influence of the lateral growth interface between waveguide and the photoabsorbing GaInAs material, the spacing d between interface and p region of the photodiode was varied between 0 and 4 mu m. The detector bandwidth is not limited by the electrical RC time constant up to frequencies of 50 GHz for devices with an active area of 10*11 mu m2. Best values for the quantum efficiency and the electrical 3 dB cutoff frequency of 65% and 8 GHz are obtained. Both decrease strongly with increased spacing d due to an enhanced diffusion component and an increase of carriers trapping and recombination effects at the growth interface. This interpretation of the experimental data was well confirmed by a detailed analysis of the dynamic device behavior based on analytical calculations of the physical transport mechanisms. Consequently, for a redesigned photodiode the distance d has to be minimized as far as possible.