Theory, glossary of the Photo Detector number of carriers generated is basically in proportion to
This document comment on the theory of the Photo the luminance of the light, and a photo current flows
Detector device and a general term. through the photodiode. The size of the photo current is
roughly proportional to the intensity of the light.
Kind of the Photo Detector
A PIN photodiode is a device that has a significantly thick
Photodiode I-layer between the PN junction. This widens the
A photodiode is a semiconductor device which converts depletion layer when a reverse bias is applied, and allows
the light to electric energy when exposed to light. It comes the diode to be used at a high reverse bias voltage. The
in a package for use as an electronic component. high electrical field conductivity in the wide depletion
layer prompts the carriers to move, and has the effect of
Characteristics of the photodiode increasing response.
1.Excellent linearity of the output current with
Ip VR
respect to incident light
2.Quick response p n
3.Wide spectral response RL
Eg (eV)
4.Long life
5.Small output change with respect to temperature
changes Electron 空乏層 正孔
6.Small output current Conduction
band
Incident light
Phototransistor .hν
A phototransistor is designed to amplify the output from a Band gap
photodiode using a transistor. Compared to the photodiode, .hν
it provides higher output signal levels.
Valence band
Characteristics of the Phototransistor
1.Large photo currents p-layer i-layer .n+-layer
2.Slow response
3.Long life h：Planck’s constant ν：Frequency of light
4.Poor output current linearity with respect to incident Eg：Energy gap
light
Fig.1 Theory of the PIN photodiode
5.Large output changes with respect to temperature
changes
Phototransistor
The phototransistor amplifies a photo current using the
Principle of Operation amplification function of a transistor, to compensate for
the low sensitivity of photodiodes and PIN photodiodes. It
Photodiode has a structure that basically combines a photodiode and a
The photodiode has a PN junction consisting of a P-type transistor Fig.2.
semiconductor region on the light receiving side and an When light strikes the depletion layer between the base
N-type semiconductor region on the substrate side Fig.1. and collector and its surrounding area, the photo current
Applying a reverse bias to the PN junction creates a that is generated becomes the base current for the
depletion layer between the P-layer and N-layer, so-called transistor and is amplified by the transistor’s amplification
because it has no mobile carriers. When light that has factor ß. However, the photo current between the base and
greater energy than the semiconductor band gap energy collector flows slowly, because it flows with the diffusion
strikes the region near the junction of the photodiode (the of the carriers. It also has a slower response than a
depletion layer and the area surrounding it), the electrons photodiode or PIN photodiode, because the large diffusion
in the valance band absorb the light and rise up to the of the carriers causes the high frequency component
conduction band, thus leaving holes in the valance band inside the photo current to short-circuit.
and generating carriers. The carriers thus generated in the
depletion layer separate due to electrical field
conductivity, so that the electrons move to the N region,
and the holes move to the P region. At this time, the
2019.9.30 1 スタンレー電気株式会社 Stanley Electric Co.,Ltd.
Incident light Photodiode
hν
Base Emitter Power Dissipation [Pd]
Power dissipated by photodiode (photo current and
.p .n reverse voltage. [mW]
.n Reverse Voltage [VR]
Reverse voltage applied from pin photodiode cathode to
the anode. [V]
Fig.2: Structure of a phototransistor
Dark Current [ID]
Current that flows to photodiode when the reverse
Glossary of Terms voltage is applied to the diode in the dark. [nA]
Surface mount Photo Detector Device(Chip Type) Photo current [IP]
The device which I put an Photo Detector die on a Current that flows from photodiode cathode to the anode
printed substrate with Photo Detector for surface by incoming light under specified conditions. [µA]
mounting it and resin sealed.
The type that kept a filter function to cut visible light in Inter-terminal capacity [CT]
sealing resin exists. The capacitance between the cathode and anode
terminals of a photodiode. [pF]
Sensitivity [S]
The amount of current that flows per energy of radiation
from a single wavelength of light. [A/W]
Phototransistor
Collector-emitter Voltage [VCEO]
Voltage applied from the phototransistor collector to the
emitter. [V]
Emitter-collector Voltage [VECO]
Reverse voltage applied from the phototransistor emitter
(Visible light cut type)
to the collector. [V]
Collector-Emitter Saturation Voltage [VCE（sat）]
Photo Detector device is common Phototransistor voltage between the collector and the
emitter under specified saturation conditions. [V]
Radiation luminance [Ee]
The radiant flux that is applied per unit area. [W/cm2] Collector Current [IC]
Maximum value of the current that flows from the
Peak Sensitivity Wavelength [λp] collector to the emitter of a Phototransistor. [mA]
Wavelength at which the photo sensitivity is the greatest.
[nm] Collector Dissipation [PC]
Power dissipated by phototransistor . [mW]
Response Time [tr/tf]
The rise (10% to 90%) and the fall (90% to 10%) time Dark Current [IC]
for peak photo current from a pulsed light source. [ns or Collector current that flows to phototransistor when
µs] forward voltage is applied to the transistor in the dark.
[µA]
Half Intensity Angle [2θ1/2]
Detection sensitivity distribution in the optical axis. Photo Current [IC]
Represented at an angle 50% of its peak value. [deg.] Phototransistor collector current that flows by incoming
light under specified conditions. [mA]
2019.9.30 2 スタンレー電気株式会社 Stanley Electric Co.,Ltd.
