2.7 Classification of X-ray Detectors
67
2.7.1.3 Semiconductor Detectors
In ionizing radiation detection physics, a semiconductor detector is a device that
uses a semiconductor as main detection material to measure the effect of incident
charged particles or photons based on p–n junction principle of the semiconductor.
The detector types mainly include silicon detectors, Silicon Drift Detector (SDD),
diamond detectors, germanium detectors, as well as cadmium telluride and cadmium
zinc telluride detectors, in which a schematic diagram of the silicon detectors is
illustrated in Fig. 2.10.
In general, the silicon detectors work by doping narrow strip of silicon to turn
them into diodes, which are then reverse biased. As charged particles pass through
the strips, they cause small ionization currents that can be detected and measured.
A thin layer of pure gold is coasted on a piece of n-type mono-crystalline silicon.
As atmospheric oxygen passes through the gold and seeps gradually into the n-type
silicon, a thin layer of p-type silicon will be brought up and p–n junction is also
produced on the opposite surface of the mono-crystalline silicon. In the interface of
the p–n junction, positive and negative charge carriers will be recombined to grow
a thin layer of high impedance without charge carriers, called depleted layer. And
thus, an electric field can be produced through the junction from the n to p. The
depleted layer is a sensitive region to detect X-ray photons. In order to increase
the thickness of the depleted layer, a reverse bias voltage is put by the electrodes
installed on two sides of the p–n junction. The higher is the reverse bias voltage, the
thicker is the depleted layer and the higher the efficiency to detect X-ray photons.
When a semiconductor is irradiated by X-ray photons, free electrons and holes will
be produced. The number of electron–hole pairs is proportional to the energy of
the radiation to the semiconductor. Under the influence of the biased electric field,
electrons and holes, respectively, travel to the electrodes, where they result in a pulse
that can be measured in an outer circuit. The holes travel in the opposite direction
Fig. 2.10 Schematic
diagram of semiconductor
detector
67
2.7.1.3 Semiconductor Detectors
In ionizing radiation detection physics, a semiconductor detector is a device that
uses a semiconductor as main detection material to measure the effect of incident
charged particles or photons based on p–n junction principle of the semiconductor.
The detector types mainly include silicon detectors, Silicon Drift Detector (SDD),
diamond detectors, germanium detectors, as well as cadmium telluride and cadmium
zinc telluride detectors, in which a schematic diagram of the silicon detectors is
illustrated in Fig. 2.10.
In general, the silicon detectors work by doping narrow strip of silicon to turn
them into diodes, which are then reverse biased. As charged particles pass through
the strips, they cause small ionization currents that can be detected and measured.
A thin layer of pure gold is coasted on a piece of n-type mono-crystalline silicon.
As atmospheric oxygen passes through the gold and seeps gradually into the n-type
silicon, a thin layer of p-type silicon will be brought up and p–n junction is also
produced on the opposite surface of the mono-crystalline silicon. In the interface of
the p–n junction, positive and negative charge carriers will be recombined to grow
a thin layer of high impedance without charge carriers, called depleted layer. And
thus, an electric field can be produced through the junction from the n to p. The
depleted layer is a sensitive region to detect X-ray photons. In order to increase
the thickness of the depleted layer, a reverse bias voltage is put by the electrodes
installed on two sides of the p–n junction. The higher is the reverse bias voltage, the
thicker is the depleted layer and the higher the efficiency to detect X-ray photons.
When a semiconductor is irradiated by X-ray photons, free electrons and holes will
be produced. The number of electron–hole pairs is proportional to the energy of
the radiation to the semiconductor. Under the influence of the biased electric field,
electrons and holes, respectively, travel to the electrodes, where they result in a pulse
that can be measured in an outer circuit. The holes travel in the opposite direction
Fig. 2.10 Schematic
diagram of semiconductor
detector