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B
EvBE
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iB
IBS
bFib
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C
vBE
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iFIES
aFiF
vBC
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iR
ICS
aRiR
vCE
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6.012 - Electronic Devices and Circuits Lecture 10 - Junction Device Wrap-up - Outline
• Announcements Handout - Lecture Outline and Summary First Hour Exam - Tomorrow!! Rm. 34-101, 7:30-9:30 pm Recitations - no recitations tomorrow but instructors will have office hours
Forward active region: vBE > 0.6 V vCE > 0.2 V
(i.e. vCB < 0.4V)iR is negligible
Other regionsCutoff:
vBE < 0.6 V Saturation: vCE < 0.2 V
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vBE +
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iBB
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vBE
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iF IES
aFiF
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aRiR
C• Review/BJT model wrap-upaFIESeqVBE/kTRev. biased junctions as sinks
or60 mV rule for diodes, BJTs bFiB
Limitations of BJT model IES
• Photodiodes and solar cells Optical and electrical excitation: superposition, iD(vAB, L)Detecting lightGenerating electrical power: optical-to-electrical conversionVideo: "Solar cell electricity is better electricity - putting 6.012 to work
improving our world (a true story)"
• Light emitting diodes; laser diodesDiode design for efficient light emission: materials, structure The LED renaissance: red, amber, yellow, green, blue, white Video: "Prof. Fonstad goes to Newton to watch the traffic lights change"Laser diodes
Clif Fonstad, 10/03 Lecture 10 - Slide 1
Bipolar transistors in history: An early bipolar integrated
circuit
Part of a series of USpostage stampscommemoratingthe decade of the1960's
C. G. Fonstad, 4/03 Lecture 10 - Slide 2
Integrated circuit bipolar transistors: An early bipolar integrated circuit
E C E BA Fairchild
Semiconductor digital (DTL) IC
from 1964
B
(before most of us were born!)
C. G. Fonstad, 4/03 Lecture 10 - Slide 3
Images courtesy of Fairchild Semiconductor. Used with permission.
BJT's, review: Looking at BJT characteristics
Regions of operation, Gummel plots (and the 60 mV rule for junctions)
•Regions of operation: forward and reverse active, saturation, cutoff
(above)
•Gummel plots and the 60 mV rule for junction diodes and BJTs (at right)
Clif Fonstad, 9/03 Lecture 10 - Slide 4
BJT's, review: Limitations of the large signal model Limitations of our junction model - their impact on BJT characteristics
We looked at this figure when we discussed our diode junction models:
•Large forward bias: High level injection (c) Series voltage drop (d)
• Large reverse bias: See Sze, S.M. Physics of Semiconductor Devices.Reverse breakdown pg. 105. ISBN 471-842-90-7.
• Very low bias levels: SCL generation and recombination (a, e)
Ref: Figure 18 in S. M. Sze,“Physics of SemiconductorDevices” 1st. Ed (Wiley,1969)
Clif Fonstad, 9/03 Lecture 10 - Slide 5
BJT's, review: Limitations of the large signal model-
•
•
Limitations of our junction model their impact on BJT characteristics
Beta roll-off at high and low collector currents
B-C junction breakdown; Clif Fonstad, 9/03 base punch through Lecture 10 - Slide 6
BJT's, review: Limitations of the large signal model Limitations of our junction model - their impact on BJT characteristics
iC
vCEvA •Base width modulation, the
Early effect and Early voltage
•Punch through: When the delpletion region at the B-C junction extends
through the base all the way to the collector (has a similar effect on the characteristics as does B-C junction reverse breakdown.
Clif Fonstad, 9/03 Lecture 10 - Slide 7
700Light emitting diodes
- human eye response
400 500 550 650 700 750
510 nm 610 nm
Viol
et
Blu
e
Gre
en
Yello
w
Ora
nge
Red
400
500
600
300
200
100
Φv:
Lum
inou
s flu
x (lm
)
450 600
C. G. Fonstad, 4/03 Lecture 10 - Slide 8
Light emitting diodes typical spectra
Relative Photon Intensity vs Wavelength • LED emission - typ. 20 nm wide
GaAsP red LED
InP • Important spectra for
comparison with LEDspectrum
Relative Spectral Response or Output vs Wavelength
C. G. Fonstad, 4/03 Lecture 10 - Slide 9
Light emitting diodes: fighting total internal reflection
Total internal reflection can be alleviated if the device is packaged in a domed shaped, high index plastic package:
If the device is fabricated with a substrate that is transparent to the emitted radiation, then light canbe extracted from the 4 sides and bottom of the device as well as from the top. This increases the extraction efficiency by a factor of 6!
C. G. Fonstad, 4/03 Lecture 10 - Slide 10
Light emitting diodes:fighting total internal
reflection, and keeping it cool (getting the light and the heat both out).
C. G. Fonstad, 4/03 Lecture 10 - Slide 11
6.012 - Electronic Devices and Circuits Lecture 10 - Junction Device Wrap-up - Summary
• BJT model wrap-upLimitations of BJT model:
@ low current levels: SCL g-r can be significant and reduce bF @ high current levels: series resistance and high level injection reduce bF w. base width modulation: iC will not truly saturate in FAR @ large vCE: B-C junction can break down and/or base punch throughDevices and model optimized for FAR
• Photodiodes and solar cellsCharacteristic: iD(vAB, L) = IS(eqvAB/kT -1) - IL
Reverse or zero bias: iD(vAB < 0) ≈ – IL (detects the presence of light) In fourth quadrant: iD x vAB < 0 (power is being produced!!)
• Light emitting diodes; laser diodesMaterials: red: GaAlAs, GaAsP, GaP amber: GaAsP
yellow: GaInN green: GaP, GaN blue: GaN white: GaN w. a phosphor
The LED renaissance: new materials (phosphides, nitrides)new applications (fibers, lighting, displays, etc)
Laser diodes: CD players, fiber optics, pointersCheck out: http://www.britneyspears.ac/lasers.htm
Clif Fonstad, 10/03 Lecture 10 - Slide 12
