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Löken, Michael
Herstellung und Charakterisierung von ultraschnellen Photodetektoren
136 S., 1999

This work reports on the fabrication and characterization of ultrafast vertical metal- silicon-metal (MSM) Schottky-barrier-photodiodes für the detection of visible and infrared light. The devices are manufactured on an epitaxial buried CoSi2 ground plate on silicon consisting of a high quality single crystalline silicon layer sandwiched between the buried CoSi2 layer and a top semitransparent metal layer. For wavelengths shorter than 1.1 µm, electron-hole pairs are generated in the Si. They are separated by an internal electrical field and accelerated towards the metal electrodes. Für shorter wavelengths, Si becomes transparent and carriers are emitted from the internal semiconductor-metal interface. A photocurrent is produced. This so-called internal photoeffect is governed by different carrier dynamics: hot electrons ar holes are injected from the metallayers into the silicon. Their large excess energy leads ta extremely fast electrical pulses. A new theoretical model für the hot carrier dynamics inside the detector is proposed and examined by detailed simulations.

The resulting temporal response of the detectors was measured with a new setup, using a modelocked Ti:sapphire laser and an optical parametric oscillator, which generates ultrafast optical pulses (170 fs ) at IR wavelengths. At 820 nm the MSM photodiodes showall impulse response as short as 3.5 ps FWHM für Si(100) and 6.7 ps FWHM für Si(lll). Für the first time, the temporal response ofMSM photodiodes was investigated at 1250 and 1560 nm wavelengths with femtosecond resolution. MSM photodiodes with different top metallization (Cr, Ti and Pt) were analyzed. In addition, the dependence of the temporal response from the applied valtage, the temperature, the dispersion on the microstrip line and the area of the detector was studied. The experimental results were interpreted with respect ta the model proposed. The Ti/Si/CoSi2 photodetectors showed an electrical pulse response of 3.2 ps FWHM at 4 V bias. This is ta our knowledge a record value. Furthermore, it is demonstrated that under certain conditions an even fast er response can be achieved. At Hat band bias (no electrical field inside the detector) a very sharp pulse of 1.2 ps was observed. Other important characteristics of the diodes ( e.g. Schottky-Barrier heights, dark current, quantum efficiency, responsivity, crystal quality of the layers) are presented.

In addition the coupling of a monomode glass fiber and a polymer-based waveguide ta the MSM photodiode on olle silicon chip was realized and investigated. The manufacturing processes are described and the experimental coupling efficiencies are glven.


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