We report a novel measurement technique for the wide-band determination of the frequency response of photodetectors. It is based upon the accurate measurement of the photocurrent noise spectra under illumination with a light-emitting diode. The high sensitivity of −200 dBm/Hz within a frequency regime from 10 MHz to 1.6 GHz renders it particularly attractive for investigating the response behavior at low optical input levels and for characterizing frequency-dependent gain phenomena. The practical potential of the method is illustrated by applying it to various types of InGaAs-based photodetectors (p-i-n and avalanche photodiodes and metal-semiconductor-metal photodetectors).

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Abstruct-The impulse response of interdigitated metalsemiconductor-metal photodetectors fabricated on an Fe-doped InGaAs absorbing layer and an Fe-doped InP barrier enhancement layer is investigated. For ultra-short pulse excitation of 150 fs at .h = G 2 0 nm the photoresponse is found to be less than 13 ps FWHM for detectors with 1 pm finger spacing. Above a certain level of illumination, the peak amplitude increases sublinearly and the relative contribution of the tail to the detector response is appreciably enhanced. The screening of the electric field by photo-generated space charges is responsible for this nonlinearity. For detectors with 5 pm finger spacing illuminated with 1.3 pm light pulses (FWHM = 33 ps), space charge perturbation of the impulse response manifests itself by a decrease of the FWHM and an increase of the fall time with increasing illumination level. The practical consequences for the performance of MSM detectors in various applications are discussed.

Articles you may be interested inInGaAs metal-semiconductor-metal photodetectors with engineered Schottky barrier heights Two-dimensional device modeling and analysis of GaInAs metal-semiconductor-metal photodiode structures High-speed GaAs metal-semiconductor-metal photodetectors with recessed metal electrodes Picosecond dynamic response of nanoscale low-temperature grown GaAs metal-semiconductor-metal photodetectors Appl.We report on passivation and antireflection coating of InP/InGaAs metal-semiconductor-metal photodetectors by low-temperature deposited silicon dioxide. The passivating performance of silicon dioxide films applied by nonreactive radio frequency magnetron sputtering and remote plasma enhanced chemical vapor deposition are comparatively investigated. Different wet chemical treatments of the InP surface prior to deposition including sulfur passivation are performed and their influences on the device performance are presented. Under optimized deposition conditions and pretreatments, both processes result in a stable and reproducible surface passivation as reflected by a drastic reduction of excessive leakage currents and photocurrent gain. The improvement of the device characteristics due to the silicon dioxide coating is attributed to a substantial lowering of the density of interface states at the insulator-InP interface as compared to nonpassivated devices.