Photoconductors (PCs) are materials whose resistance decreases upon illumination
with light. They should not be confused with photodiodes or solar cells, which can
produce an EMF or short circuit current in response to the absorption of light quanta.
Uses of photoconductors include exposure meters for cameras, light sensors in spectrophotometers,
light sensors in a variety of counting systems where an object interrupts
a light beam hitting the photoconductor, systems which sense a decrease of overall
ambient illumination and turn on outside lighting (of course, the lighting must not be
sensed by the photoconductor), oil burner safety systems and burglar alarms. PCs are
also called light dependent resistors or photoresistors. Figure 6.5 illustrates the cross-sectional
schematic of a typical PC device. Note that it is a thin wafer.
PCs can be made from a number of intrinsic as well as doped semiconductor materials.
Each semiconductor has a distinct spectral response to light, ranging UV–FIR. Absorption
of light quanta with a certain energy range by semiconductor substances produces
electron hole pairs, which enter the conduction band and drift in an applied electric
field, contributing to the current passing through the semiconductor. Greatest
Photoconductors (PCs) are materials whose resistance decreases upon illuminationwith light. They should not be confused with photodiodes or solar cells, which canproduce an EMF or short circuit current in response to the absorption of light quanta.Uses of photoconductors include exposure meters for cameras, light sensors in spectrophotometers,light sensors in a variety of counting systems where an object interruptsa light beam hitting the photoconductor, systems which sense a decrease of overallambient illumination and turn on outside lighting (of course, the lighting must not besensed by the photoconductor), oil burner safety systems and burglar alarms. PCs arealso called light dependent resistors or photoresistors. Figure 6.5 illustrates the cross-sectionalschematic of a typical PC device. Note that it is a thin wafer.PCs can be made from a number of intrinsic as well as doped semiconductor materials.Each semiconductor has a distinct spectral response to light, ranging UV–FIR. Absorptionof light quanta with a certain energy range by semiconductor substances produceselectron hole pairs, which enter the conduction band and drift in an applied electricfield, contributing to the current passing through the semiconductor. Greatest
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