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I dedicate this work to my beloved father Syed WaqarKazmi (Late), siblings

and the ummah...

Engr.Syed Absar Kazmi (Pakistan)0060-182391572

G1220119 MSEE, IIUM Malaysiaengrabsarkazmi@gmail.com

A Comprehensive Presentation on

" Photo detectors"

Semiconductor Devices (ECE 6317)Lecturer Dr.Fadzlin Hasbullah

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Outline• Elements Periodic Table• Classifications of Opto Electronics• History of Opto Detectors• Photo detection principle• Modes of Operation of Optical Detector• Law of Conservation and Optical Absorption• Types of Photo Detectors (w.r.t PN junction)

a) Photo Diode

b) PIN photo Diode

c) Avalanche Photo Diode

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Semiconductors

Table. 1. Periodic Table [1].

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Classification of optoelectronics

semiconductor devices

Figure. 1. Classification of semiconductor devices [2].

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• John N. Shive was an American physicist and inventor who made remarkable contributions in solid state physics and electronic engineering during the early days of development of transistors at the Bell Telephone Laboratories.

• Graduation in physics and chemistry in the year 1934 and PhD in the year 1939.

• In 1948 the Shive implicated light beam instead of emitter terminal as wire for transistor, generating holes that flow via collector; latterly this device was appellated as phototransistor [3].

History

Figure. 2. Phototransistor inventorAccessed on 27 Mar 15.

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What is Photo-detector ?

• Semiconductor devices which can be implicated to detects the photons presence. Such devices are known as photo detectors [5].

• They transform optical signals into electrical signals.

• When excess electrons and holes are generated in a semi-conductor.

• Response is proportional to the power in the beam.

Figure.3. Photo detectors [6].

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Photodetection principle is based on two types of photoelectric effects which are as follows [4].

External photoelectric effect : Electrons become free from the metal surface by energy absorption obtained by streams of incident photons. Photomultiplier tube and vacuum photodiode are the implications of external photoelectric effect.

Internal photoelectric effect : Free charge carriers are generated by absorption of incident photons in semiconductor junctions detectors.PIN photodiode, pn junction photodiode and avalanche photodiode.

• Important detector properties are responsivity, spectral response, and rise time.

Principles of Photodetection

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Operation regimes of an illuminated junction

Figure.4(a) .(photo detector)

Power is delivered tothe device by the external circuit [7].

Figure 4(b). Photovoltaic

Power is delivered to the load by the device(solar cell/ energy harvesting) [7].

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Modes of Operation Photoconductive vs. Photovoltaic

A photodiode can be operated in one of two modes:

Photoconductive (reverse bias)

• The photo detectors are operated in photo conductive mode.

Photovoltaic (zero-bias).

• Solar cells are operated in Photo voltaic mode.

• The photo diodes implicated in electrical energy generation are optimized to have high efficiency of energy conversion.

• The photo diodes used as photo detectors are optimized to have fast response times [8, 9].

Figure. 5. Operating Modes [10].

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Photoconductive mode

• In photoconductive mode the diode is operated in reverse biased, which interns dramatically reduce the response time at the expense of increased noise. Consequently faster response times can be achieved by increasing the depletion layer and decreasing the junction's capacitance [11].

• The photocurrent is linearly proportional to the luminance for the given spectral distribution.

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Photovoltaic Mode

• This mode exploits the photovoltaic effect, which

is the fundamental for solar cells. When used in

zero bias or photovoltaic mode, the flow of

photocurrent out of the device is restricted and a

voltage builds up [11].

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Characteristic curve for operating modes

Figure. 6. Photo detectors operating modes [11].

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Current Voltage characteristic

Figure.7. Photodiode Characteristic curves [12].

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Light spectrum versus wavelength and energy.

Figure. 8. Light spectrum vs. wavelength and energy [13].

Figure.9. Momentum conservation law

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MOMENTUM CONSERVATION LAW

Momentum conservation ensures that only vertical transitions are allowed during absorption and emission.

Figure.9 Depicts Band-to-band absorption in semiconductors.

An electron from the valence-band going to an acceptor causes a hole to be generated. Reverseprocesses can also occur.

The most imperative mechanism for recombination and generation is light emission and absorption respectively [14].However my concern is in absorption.

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Optical Absorption in Semiconductors

• Interaction in semiconductors as far as devices are concerned is the band-to-band transition.

• In the photon absorption process, a photon scatters an electron in the valence band, causing the electron to go into the conduction band.

• These two processes are of obvious importance for light-detection [14].

Figure.10. absorption and recombination [15].

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•–

• Most modern photo detectors operate on the basis of the internal photoelectric effect.

•The photo excited electrons and holes remain within the material, increasing the electrical conductivity of the material in a semiconductor.

•Electron-hole photogenerationin semiconductor

Absorbed photons generate free electron-hole pairs.

Transport of the free electrons and holes upon an electric field results in a drift current [7].

Electron-hole photo generation

Figure.11. Photo generation process

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Absorption coefficient of some direct and indirect gap

semiconductors.

For the direct gap material, the absorption coefficient is very strong once the photon energy exceeds the band gap.

For indirect materials the absorption coefficient is small near the band edge, but once the photon energy is more than the direct gap, the absorption coefficient increases rapidly [14].

Figure.12. Absorption coefficient for semiconductors.

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Absorption Coefficient and Photodiode Materials

– –

Photon absorption in a direct and indirect band gap semiconductors [16].

Direct Band gap

E

CB

VB

kk

Eg

EC

EV

Photon

Figure.13(a).direct band gap

k

Indirect Band gap

E

k

VB

CB

Photon

Phonons

EgEC

EV

Figure.13(b).indirect band gap

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Responsivity vs. wavelength

Figure.12. . Typical responsivity curves for silicon, InGaAs, and germanium [29].

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Photo detectors Significant parameters

• Some of the imperative parameters of photo detector are as follows [18].

Quantum Efficiency It is the ratio of primary electron-hole pairs created photon to the photon incident on the diode material.

• Detector Responsivity This is the ratio of output current to input optical power. Hence this is the efficiency of the device. The unit of responsivity is amperes per watt.

• Spectral Response Range This is the range of wavelengths over which the device will operate. The spectral response refers to the curve of detector responsivity as a function of wavelength

• Noise Characteristics

• The level of noise produced in the device is critical to it operation at low levels of input light.

• Response Time

• This is a measure of how quickly the detector can respond to variation in the input light intensity

• Rise time

The rise time is the time for the detector output current to change to change from 10 to 90% of its final value when the optic input power variation is a step.

• Gain

The APDs have more gain than PIN diode due to the effect of impact ionization as it is operated at high electric field

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Types of photo detector (pn junction)

• Photodiode

• P-I-N Photodiode

• Avalanche Photodiode

Figure.15. Photodiodes [ 19].

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Photo diode

• Photo means light and diode means a device pertaining of two electrodes [20].

• A photo diode is a light sensitive electronic device capable of converting light into a voltage or current signal.

• It works on the principle of photo generation.

Figure. 16. Photodiode [21]

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Photodiode Equivalent Circuit

The simplified photodiode equivalent model represents the key elements.

• The irradiance (light intensity) is proportional current source ID which is in parallel with diode in figure 17.

• Performance is dependent upon parasitic components RD and CD can plays an imperative role [22].

Figure. 17. Photodiode Equivalent circuit

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Working of photodiode is based on Internal photoelectric effect : Free charge carriers are generated by absorption of incident photons in semiconductor junctions detectors [4].

The diode is connected reverse biased under incident photons.

•Free charge carriers are created by photon absorption.

•The pair of electron and hole is generated by every single incident photon.

•These moving charges cause current flow through the external circuit [23].

Photodiode Working

Figure. 18. Photodiode in reverse biased

Figure.18. Photodiode energy band dgm [24].

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The reverse biased photo diode is under luminance (incident photons) is represents the energy bandgap diagram in figure. 18(b) and 18(c).

• which absorbed in the junction via window.

• The absorbed energy raises a bound electron across the band gap from the valence to the conduction band.

• A free hole is left in the valence to the conduction band.

• under electric field the generated free charge

carrieirs produce the drift current.

Photodiode Working...

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P-I-N photodiode• A PIN diode is a diode with a wide, lightly

doped 'near' intrinsic semiconductor region between a p-type semiconductor and an n-type semiconductor region.

• The p-type and n-type regions are typically heavily doped because they are used for ohmic contacts [11].

Figure. 19. PIN diode

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P-I-N photodiode.....

Figure.20 (d). Photodiode Energy Band Dgm [16].

Figure. 20 (a). PIN diode [24]. Figure. 20 (b). PIN diode [24]. Figure. 20 (c). PIN diode [24].

Figure. 20.a shows the biased PIN photodiode vs. energy band diagram.Figure. 20.b depicts reversed biased PIN photodiode. Figure. 20.c represents construction layers of PIN.Figure. 20.d shows descriptive energy band diagram.

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Generic Operating Parameters of an pin Photodiode InGaAs

Table. 2. PIN Photodiode operating parameters [25].

Avalanche Photodiode• Avalanche Photodiodes ( APDs ) are high sensitivity, high

speed semi-conductor "light" sensors.

• Compared to regular PIN construction photodiodes, APDs, have an internal region where electron multiplication occurs, by application of an external reverse voltage, and the resultant "gain" in the output signal means that low light levels can be measured at high speed.

• Incident photons create electron – hole pairs in the depletion layer of a silicon photodiode structure and these move towards the respective PN junctions depending on the electric field strength.

Figure. 21(a). APD construction [27].

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Avalanche Photodiode

Figure. 21(c). APD characteristic curve [26].

Describing Avalanche photo-detecter construction and current voltage characterstic curve with higlighted circle, depicts avalauche region in figure.21(a) and 21(b) accordingly.Operated with much higher reverse bias. •This allows each photo-generated carrier to be multiplied by avalanche breakdown.•The effect is known as impact ionization/avalaunche effect.•Resulting in internal gain within the photodiode, which increases the effective  responsivity of the device.

Figure. 21(b). Typical parameters for semiconductors [29]

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Significance of Photodiodes

• Photodiodes are unique among light detectors in that when illuminated, they generate an output which is proportional to light level. Their characteristics and features can be summarized as follows [8]:

Low cost visible and near-IR photo detector

• Excellent linearity in output photocurrent according to light intensity

• Fast response times.

• Available in a wide range of packages

• Low noise

• Mechanically rugged yet compact and light weight

• Available as duals, quads or as linear arrays

• Usable with almost any visible or near infrared light source such as LEDs; neon, fluorescent, incandescent bulbs; lasers; flame

• sources; sunlight; etc.

Figure.22. Applications of photodiodes [28].

• Spectroscopy.

• Photography.

• Analytical instrumentation.

• Optical position sensors.

• Beam alignment.

Silicon photodiodes are utilized in such diverse implications as

• Surface characterization.

• Laser range finders.

• Optical communications.

• Medical imaging instruments.

Qur’an about Light• It is He who made the sun a shining light and the moon a

derived light and determined for it phases - that you may know

the number of years and account [of time]. Allah has not

created this except in truth. He details the signs for a people

who have knowledge [10:5].

• Indeed, in the alternation of the night and the day and [in] what

Allah has created in the heavens and the earth are signs for a

people who fear Allah [10:6].

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References [1].

[2].

[3] www.circuitstoday.com/invention-history-of-phototransistor-and-photodiode,Acessed 27 mar.[4] [5] [6] http://www.roithner-laser.com/pd/pd_ingaas.html[7] Photo Devices by Jia-Ming ch#14 and Fundamental of Photonics 2nd Edition by Saleh & Teich ch#18.

[8] http://ecetutorials.com/analog-electronics/photo-diode/Accessed on 22 Mar 2015.[9]

[10] http://sub.allaboutcircuits.com/images/quiz/01031x01.png Accessed on 29 Mar 2015.

[11] [12][13]

www.powershow.com/view4/5accff-Mjk4Z/Single_Photon_Detectors_powerpoint_ppt_presentation

Opto Electronic Device March, 2003 20th Edition Issued by Matsushita Electric Industrial Co., Ltd.(C) Matsushita Electric Industrial Co., Ltd

www.powershow.com/view1/1b295a-ZDc1Z/Chapter_7_Light_Detectors_powerpoint_ppt_presentation 28 marSemiconductor Physics and Devices Basic Principles Fourth Edition Donald A. Neamen University of New Mexico

http://www.thorlabs.com/tutorials.cfm?tabID=31760 Accessed on 28 Mar 2015.

National seminar on Electric Energy : Safety & Conservations Department of Physics, University of Delhi India

http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/photdet.html#c2

BOOK; Semiconductor Physics and Devices Basic Principles Fourth Edition Donald A. Neamen University of New Mexico ,Ch # 14 ,Pg # 622.

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References.... [14].

[15]

[16]

[17]

[18]

[19]

[20]

[21]

[22]

[23]

[24]

BOOK; Device Physics and Design by UMESH K. MISHRA and JASPRIT SINGH , USA

http://chemwiki.ucdavis.edu/Analytical_Chemistry/Analytical_Chemistry_2.0/10_Spectroscopic_Methods/10A%3A_Overview_of_Spectroscopy Accessed on 27 Mar 2015.

http://www.powershow.com/view/3d4ae1-MWFhN/Chap_5_Photodetectors_powerpoint_ppt_presentation

http://pongsak.ee.engr.tu.ac.th/le426/doc/OptCommC6.pdf Accessed on 22 Mar 2015.

http://pongsak.ee.engr.tu.ac.th/le426/doc/OptCommC6.pdf Accessed on 21 Mar 2015.

http://www.pro-lite.co.uk/File/germanium_detectors.php Accessed on 29 Mar 2015

http://ecetutorials.com/analog-electronics/photo-diode/Accessd on 21 Mar 2015

http://mcututor.blogspot.com/2012/02/photo-diodes-symbol.html Accessed on 29 Mar 2015

http://e2e.ti.com/blogs_/archives/b/thesignal/archive/2012/08/06/illuminating-photodiodes 29 Mar 2015

http://www.powershow.com/view1/1b295a-ZDc1Z/Chapter_7_Light_Detectors_powerpoint_ppt_presentation 28 marhttp://educypedia.karadimov.info/library/Photodetectors-leture-12-03-09.pdf Accessed on 29 Mar 2015.

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References... [25]

[26]

[27]

[28]

[29]

http://pongsak.ee.engr.tu.ac.th/le426/doc/OptCommC6.pdfaccessed on 22 Mar 2015

https://www.thorlabs.com/images/TabImages/Single_Photon_Counting_Technique-300.png Accessed on 29 Mar 2015.

http://www.pacer.co.uk/Assets/Pacer/User/Photodiode%20Typical%20Applications.pdf 27 Mar 2015.

http://www.osioptoelectronics.com/application-notes/AN-Photodiode-Parameters-Characteristics.pdf

http://download.springer.com/static/pdf/788/chp%253A10.1007%252F978-1-4419-0304-4_6.pdf?auth66=1427799079_3ead44b750ec7155543d1f0d8122825d&ext=.pdf Accessed on 31 Mar 15

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