Electronic Devices and Circuits Lecture 10 - Junction Device Wrap-up - Outline Announcements IES

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1 Electronic Devices and Circuits Lecture 10 - Junction Device Wrap-up - Outline Announcements Handout - Lecture Outline and Summary First Hour Exam - Tomorrow!! Rm , 7:30-9:30 pm Recitations - no recitations tomorrow but instructors will have office hours Review/BJT model wrap-up vbc vbc ICS ICS Rev. biased junctions as sinks afiese bfib qvbe/kt + + ir is negligible ib or afif afif ir ir vce B ib 60 mv rule for diodes, BJTs bfib BB + + if if B + + Limitations of BJT model IES IES IBS arir arir vbe vbe vbe IES vbe CC + Forward active region: vbe > 0.6 V vce > 0.2 V (i.e. vcb < 0.4V) Other regions Cutoff: vbe < 0.6 V Saturation: vce < 0.2 V Photodiodes and solar cells E E Optical and electrical excitation: superposition, i D (v AB,L) Detecting light Generating electrical power: optical-to-electrical conversion Video: "Solar cell electricity is better electricity - putting to work improving our world (a true story)" Light emitting diodes; laser diodes Diode 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 C C E E

2 Bipolar transistors in history: An early bipolar integrated circuit Part of a series of US postage stamps commemorating the decade of the 1960's C. G. Fonstad, 4/03 Lecture 10 - Slide 2

3 Integrated circuit bipolar transistors: An early bipolar integrated circuit B Images courtesy of Fairchild Semiconductor. Used with permission. E C E B A Fairchild Semiconductor digital (DTL) IC from 1964 (before most of us were born!) C. G. Fonstad, 4/03 Lecture 10 - Slide 3

4 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

5 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: Reverse breakdown pg ISBN Very low bias levels: SCL generation and recombination (a, e) See Sze, S.M. Physics of Semiconductor Devices. Ref: Figure 18 in S. M. Sze, Physics of Semiconductor Devices 1st. Ed (Wiley, 1969) Clif Fonstad, 9/03 Lecture 10 - Slide 5

6 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

7 BJT's, review: Limitations of the large signal model Limitations of our junction model their - impact on BJT characteristics i C v A Base width modulation, the Early effect and Early voltage v CE 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

8 700 Light emitting diodes - human eye response 600 Φv: Luminous flux (lm) nm 610 nm Violet Blue Green Yellow Orange Red C. G. Fonstad, 4/03 Lecture 10 - Slide 8

9 Light emitting diodes typical spectra LED emission - typ. 20 nm wide GaAsP red LED Relative Photon Intensity vs Wavelength Important spectra for comparison with LED spectrum InP Relative Spectral Response or Output vs Wavelength C. G. Fonstad, 4/03 Lecture 10 - Slide 9

10 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 can be 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

11 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

12 Electronic Devices and Circuits Lecture 10 - Junction Device Wrap-up - Summary BJT model wrap-up Limitations of BJT low current levels: SCL g-r can be significant and reduce b high current levels: series resistance and high level injection reduce b F w. base width modulation: i C will not truly saturate in large v CE : B-C junction can break down and/or base punch through Devices and model optimized for FAR Photodiodes and solar cells Characteristic: i D (v AB,L)=I S (e qv AB/kT -1) - I L Reverse or zero bias: i D (v AB < 0) I L In fourth quadrant: i D x v AB < 0 Light emitting diodes; laser diodes (detects the presence of light) (power is being produced!!) Materials: 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, pointers Check out: Clif Fonstad, 10/03 Lecture 10 - Slide 12

Microelectronic Devices and Circuits Lecture 8 - BJTs Wrap-up, Solar Cells, LEDs - Outline

6.012 - Microelectronic Devices and Circuits Lecture 8 - BJTs Wrap-up, Solar Cells, LEDs - Outline Announcements Exam One - Tomorrow, Wednesday, October 7, 7:30 pm BJT Review Wrapping up BJTs (for now)