Photoconductive mode

Due to the small size and applied bias voltage (when used in photoconductive mode) the response time of each diode element in the PDA can be very fast indeed, so total integration times can also be short, hi principle, data rates of 200 spectra per second are achievable, but in reality spectral co-adding is a more sensible objective, to improve overall SNR. 

If, however, a reverse bias is applied across the junction, then the conductance is greatly increased thereby producing a current which is proportional to the light flux. This mode of operation is called the photoconductive mode. 

Indium arsenide and germanium photodiodes Indium arsenide photodiodes are used for the near-infrared region and typically cover 1800-3600 nm. They are destroyed by bias voltages in excess of 1V and are only separated in the photoconductive mode. They have a fast rise time ( 100 ns) and give excellent... 

For the detection of fast and weak signals, the photoconductive mode is best suited. In this mode the diode is provided with a bias voltage which reduces the p-n junction capacity, and thus increases the cut-off frequency. 

Photoconductive polymers can be convenientiy classified into five categories based on thek stmctures and modes of photoconduction. 

The photoconductive properties of the fluorene-derived polymers 19, 23, and 24 were studied by the single-layer photocells in the configuration of ITO/Pt polyyne/Al. These polymers show moderate photoconductivity. A PCQE of 0.01 % was estimated in these cases, which does not vary much with variation of the central fluorene ring.26,30 Likewise, polymer 44 was also shown to be a photoconducting material in a similar architecture with a PCQE of 0.01 % in the forward bias mode. 

In the photoconductive sensor, the electrode is ohmic where carrier replenishment occurs. Electron photoconductivity is the dominant mode. In this case, the photocurrent is a secondary current. Photocurrent and photoconductive gain are given by (Bube, 1961)... 

A short time later, Levin s group modified step-scan FT-IR spectrometer to operate with a mid-IR MCT FPA detector. Unlike most MCT detectors used in FT-IR spectrometers, which operate in the photoconductive (PC) mode, the pixels of MCT FPA detectors operate in the photovoltaic (PV) mode. As noted in Section 1.2.2, the cut-off wavenumber of narrow-band PC MCT detectors is about 750 cm" . The PV detector elements used in MCT FPA detectors have the same high sensitivity as narrow-band PC MCT detectors, but the cut-off wavenumber is higher, at about 850 cm" . 

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