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Lundstrom ECE 305 S15
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
OE devices
3
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)
Lundstrom ECE 305 F14
Classification
4 Lundstrom ECE 305 F14
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
5
λ (𝜇𝑚)=1.24/ 𝐸↓𝐺 (𝑒𝑉) Light to electricity
Electricity to light
Photo-detectors
Lundstrom ECE 305 S15 6
photodiodes
7
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
9
−ID VR( )
λ →
Eph = hf > EG
fλ = c
λ = 1.24Eph eV( )
QE = IDIin
≤1
Lundstrom ECE 305 F14
PIN photodiodes
10
i-Semiconductor
N+ P+
Lundstrom ECE 305 F14
PIN photodiodes
11
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?
Lundstrom ECE 305 S15 13
Classification
14 Lundstrom ECE 305 F14
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
15
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
16
λ (𝜇𝑚)=1.24/ 𝐸↓𝐺 (𝑒𝑉) Light to electricity
Electricity to light
Determine Eg for color …
Lundstrom ECE 305 S15 17
λ (𝜇𝑚)=1.24/ 𝐸↓𝐺 (𝑒𝑉)
Red (0.65 𝜇𝑚); Green (0.57 𝜇𝑚); Blue (0.45 𝜇𝑚)
Classification
18 Lundstrom ECE 305 F14
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
Lundstrom ECE 305 S15 19
Operation of a Laser
Lundstrom ECE 305 S15 20
Inverse relationship between indices and bandgaps is the key
21
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?
Lundstrom ECE 305 S15 22
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?
Lundstrom ECE 305 S15 23
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.
Lundstrom ECE 305 S15 24