Photodiode working principle characteristics and applications

Photodiode Working Principle,
Characteristics and
Applications

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Characteristics and Applications
Introduction:
 A photodiode is a PN-junction diode that consumes light energy to
produce electric current. Sometimes it is also called as photo-detector, a light
detector, and photo-sensor. These diodes are particularly designed to work in
reverse bias condition, it means that the P-side of the photodiode is
associated with the negative terminal of the battery and n-side is connected
to the positive terminal of the battery.

 A photodiode is one type of light detector, used to convert the light into
current or voltage based on the mode of operation of the device.
 It comprises of optical filters, built-in lenses and also surface areas.
 These diodes have a slow response time when the surface area of the
photodiode increases.
 Photodiodes are alike to regular semiconductor diodes.
What is a Photodiode

 They may be either visible to let light reach the delicate part of the device.
 Several diodes intended for use exactly as a photodiode will also use a PIN
junction somewhat than the usual PN junction.

 Some photodiodes will look like a light emitting diode.
 They have two terminals coming from the end.
 The smaller end of the diode is the cathode terminal.
 While the longer end of the diode is the anode terminal.

 See the following schematic diagram for the anode and cathode side.
Under forward bias condition, conventional current will flow from the
anode to the cathode, following the arrow in the diode symbol.
 Photocurrent flows in the reverse direction.

Photodiode

Types of Photodiode
 Although there are numerous types of photodiode available in the
market .
 They all works on the same basic principles, though some are improved
by other effects.
 The working of different types of photodiodes work in a slightly different
way.
 But the basic operation of these diodes remains the same.

• PN Photodiode
• Schottky Photo Diode
• PIN Photodiode
• Avalanche Photodiode
Types of Photodiode
 The types of the photodiodes can be classified based on its construction
and functions as follows.

Types of Photodiode
 These diodes are widely used in different applications .
 where the detection of the presence of light, colour, position, intensity
is required.

Types of Photodiode
• The linearity of the diode is good with respect to incident light
• Noise is low.
• The response is wide spectral
• Rugged mechanically
• Light weight and compact
• Long life
 The main features of these diodes include the following.

 The required materials to make a photodiode and the range of
electromagnetic spectrum wavelength range includes the following
• For silicon material: The electromagnetic spectrum wavelength range
will be (190-1100) nm
• For Germanium material: The electromagnetic spectrum wavelength
range will be (400-1700) nm
• For Indium gallium arsenide material: The electromagnetic spectrum
wavelength range will be (800-2600) nm
Materials to Make a Photodiode

Materials to Make a Photodiode
• For Lead (II) sulfide material: The electromagnetic spectrum
wavelength range will be <1000-3500) nm
• For Mercury, cadmium Telluride material: The electromagnetic
spectrum wavelength range will be (400-14000) nm
 Because of their better band gap, Si-based photodiodes produce
lower noise than Ge-based photodiodes.

Working of Photodiode
 When a photon of ample energy strikes the diode.
 It makes a couple of an electron-hole.
 This mechanism is also called as the inner photoelectric effect.
 If the absorption arises in the depletion region junction.
 Then the carriers are removed from the junction by the inbuilt electric
field of the depletion region.

 The holes in the region move toward the anode, and electrons move
toward the cathode, and a photocurrent will be generated.
 The entire current through the diode is the sum of the absence of light
and the photocurrent.
 So the absent current must be reduced to maximize the sensitivity of the
device.

PN Junction Diode

Modes of Operation
 The operating modes of the photodiode include three modes, namely
• Photovoltaic mode.
• Photoconductive mode.
• Avalanche diode mode.

Photovoltaic Mode:
 This mode is also known as zero bias mode.
In which a voltage is produced by the lightened photodiode.
 It gives a very small dynamic range & non-linear necessity of the voltage
formed.

Photoconductive Mode
 The photodiode used in this photoconductive mode is more usually
reverse biased.
 The reverse voltage application will increase the depletion layer’s width.
 Which in turn decreases the response time & the junction capacitance.
 This mode is too fast and displays electronic noise.

Avalanche Diode Mode
 Avalanche diodes operate in a high reverse bias condition.
 which permits multiplication of an avalanche breakdown to each
photo-produced electron-hole pair.
 This outcome in an internal gain in the photodiode, which slowly
increases the device response.

V-I Characteristics of Photodiode
 A photodiode continually operates in a reverse bias mode.
 The photocurrent is nearly independent of reverse bias voltage which is
applied.
 For zero luminance, the photocurrent is almost zero excluding for small
dark current.

 It is of the order of nano amperes.
 As optical power rises the photo current also rises linearly.
 The max photocurrent is incomplete by the power dissipation of the photo
diode.

 The characteristics of the photodiode are shown clearly in the following
figure.

Applications of Photodiode
 The applications of photodiodes involve in similar applications of
photodetectors like charge-coupled devices, photoconductors, and
photomultiplier tubes.
 These diodes are used in consumer electronics devices like smoke
detectors, compact disc players, televisions and remote controls in VCRs.
 It uses in consumer devices like clock radios, camera light meters, and
street lights.

 Photoconductors are more frequently used rather than photodiodes.
 Photodiodes are frequently used for exact measurement of the intensity
of light in science & industry.
 Generally, they have an enhanced, more linear response than
photoconductors.

 Photodiodes are also widely used in numerous medical applications like
instruments to analyze samples, detectors for computed tomography and
also used in blood gas monitors.
 These diodes are much faster & more complex than normal PN junction
diodes.
 It is frequently used for lighting regulation and in optical communications.

 A photodiode is a kind of light detector, which involves the
conversion of light into voltage or current, based on the mode
of operation of the device. A photodiode is a semi-conductor device,
with a p-n junction and an intrinsic layer between p and n layers.
Conclusion

Photodiode working principle characteristics and applications

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Photodiode working principle characteristics and applications