A bipolar transistor with its base-collector junction acting as a
photodiode, which, if irradiated, controls the response of the device. Due to the inherent current
gain (of the transistor) the responsivity of the phototransistor is greater than that
of photodiodes. A Darlington phototransistor consists of two separate transistors
coupled in the high-
impedance Darlington configuration with a phototransistor as the input transistor. A field
effect phototransistor or photo-
FET is a
field effect transistor (
FET) that employs photogeneration of carriers in the
channel region (the neutral region sandwiched between the insulator and the depletion region
under the gate of the
FET). It is characterized by high responsivity due to the high current gain of the
FET.
Source:
PAC, 1995, 67, 1745
(Nomenclature, symbols, units and their usage in spectrochemical analysis-XI. Detection
of radiation (IUPAC Recommendations 1995))
on page 1755