ECE-305: Spring 2015 Optoelectronic Devices Professor Mark Lundstrom Electrical and Computer Engineering Purdue University, West Lafayette, IN USA [email protected]3/22/15 Pierret, Semiconductor Device Fundamentals (SDF) pp. 347-368 Objective Explain that there are two types of optoelectronic devices. Differentiate a solar cell vs. photodetector Differentiate PIN vs. avalanche photodetectors Differentiate LED vs. lasers Explain why you can make a Si photodetector, but not a Si laser. Lundstrom ECE 305 S15 2
Transcript
Lundstrom ECE 305 S15
ECE-305: Spring 2015
Optoelectronic Devices
Professor Mark Lundstrom Electrical and Computer Engineering
Pierret, Semiconductor Device Fundamentals (SDF) pp. 347-368
Objective
§ Explain that there are two types of optoelectronic devices.
§ Differentiate a solar cell vs. photodetector § Differentiate PIN vs. avalanche
photodetectors § Differentiate LED vs. lasers § Explain why you can make a Si
photodetector, but not a Si laser.
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OE devices
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1) Photodiodes (SDF, pp. 349-352) 2) PIN photodiodes (SDF, pp. 352-355) 3) Avalanche photodetectors (SDF, pp. 355-356) 4) LED’s (SDF, pp. 361-368) 5) Lasers 6) Solid state lights 7) Solar cells (SDF, pp. 356-361)
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Classification
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Light to electricity Solar cell Si, CdTe Photodetector PIN, Avalanche CCD, CMOS, Leaf
Electricity to light
LED Blue, Green, Red Solid state light Lasers Pointer, continental drift
Wavelength vs. Bangap energy
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λ (𝜇𝑚)=1.24/ 𝐸↓𝐺 (𝑒𝑉) Light to electricity
Electricity to light
Photo-detectors
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photodiodes
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EC
EC
x
q Vbi +VR( )
+VR −EV
Fn
Fp
ID
photodiodes
8
EC
EC
x
q Vbi +VR( )
+VR −EV
Fn
Fp
ID
spectral response
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−ID VR( )
λ →
Eph = hf > EG
fλ = c
λ = 1.24Eph eV( )
QE = IDIin
≤1
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PIN photodiodes
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i-Semiconductor
N+ P+
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PIN photodiodes
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EC
EC
x
q Vbi +VR( )
+VR −EV
Fn
Fp
ID
avalanche PIN photodiodes
12
EC
EC
x
q Vbi +VR( )
+VR −EV
Fn
Fp
ID
Questions
What type of detectors do you use to take selfies? If a leaf is a energy harvester, then why is it green? A CCD camera has higher resolution than CMOS imagers. Explain. Why can’t you use Si photodetector in an optical network?
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Classification
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Light to electricity Solar cell Si, CdTe Photodetector PIN, Avalanche CCD, CMOS, Leaf
Electricity to light
LED Blue, Green, Red Solid state light Lasers Pointer, continental drift
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N+ P
LED’s
E = hf = EG
QE = number of photons per sec outnumber of electrons per sec in
= τ nrτ nr +τ r
Wavelength vs. Bangap energy
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λ (𝜇𝑚)=1.24/ 𝐸↓𝐺 (𝑒𝑉) Light to electricity
Electricity to light
Determine Eg for color …
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λ (𝜇𝑚)=1.24/ 𝐸↓𝐺 (𝑒𝑉)
Red (0.65 𝜇𝑚); Green (0.57 𝜇𝑚); Blue (0.45 𝜇𝑚)
Classification
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Light to electricity Solar cell Si, CdTe Photodetector PIN, Avalanche CCD, CMOS, Leaf
Electricity to light
LED Blue, Green, Red Solid state light Lasers Pointer, continental drift
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Operation of a Laser
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Inverse relationship between indices and bandgaps is the key
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N+ P
lasers R
= 100%
R = 99.9%
i) Spontaneous recombination: Rr =Δnτ r
Fabry-Perot cavity
ii) Stimulated recombination (Einstein)
What is wrong with this picture?
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Review Questions
§ What are the two types of optoelectronic devices we discussed today?
§ Why type of detectors do you have in your i-phone? How does this differ from the other type of photodetector?
§ What innovation in LED was honored with a Nobel Prize in physics last year?
§ What is the difference between light coming out of a laser vs. that from a LED?
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Conclusions
A very exciting field – has implications for energy, communications, physics, medicine, etc.
Simple p-n junction physics explains most of the phenomena; lasers require one additional equation for light intensity.
