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OPTI 202L Lab # 12 – p-n Junctions: Photodiodes, Solar Cells LED’s, and Laser Diodes

OPTI 202L Lab # 12 – p-n Junctions: Photodiodes, Solar Cells LED’s, and Laser Diodes. Dr. Mike Nofziger Professor College of Optical Sciences University of Arizona.

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OPTI 202L Lab # 12 – p-n Junctions: Photodiodes, Solar Cells LED’s, and Laser Diodes

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  1. OPTI 202LLab #12 – p-n Junctions: Photodiodes, Solar CellsLED’s, and Laser Diodes Dr. Mike Nofziger Professor College of Optical Sciences University of Arizona Dr. Mike Nofziger 2014

  2. Lecture #12 Outline:●Photodiodes—Physical Construction—Basic Properties—Basic Physics—Current Voltage Characteristics—Use in an Electrical Circuit●Solar Cells—Basic Properties●LED’s—Basic Properties Dr. Mike Nofziger 2014 Lecture 12

  3. Photodiodes—Physical Construction: “Official Symbol” A 40 Gb/s “Optical Receiver” !! Dr. Mike Nofziger 2014 Lecture 12

  4. ● p-n junction (p-side ≡ “anode”, n-side ≡ “cathode”)● Built-in electric field (depletion region) separates the electrons and holes (electrons → p-side, holes → n-side) ● Photons absorbed (ideally in or near the depletion region) create electron-hole pairs ● Built-in electric field separates the electrons and holes before they recombine, producing a photocurrent (electrons → n-side, holes → p-side)● I-V curve is very non-linear ● The photocurrent is linear with photon flux over 7-decades! ●Most common semiconductor material used to make photodiodes (for detection of visible light) is Silicon (Si). Photodiodes—Basic Properties: Dr. Mike Nofziger 2014 Lecture 12

  5. Photodiodes—Basic Physics: Dr. Mike Nofziger 2014 Lecture 12

  6. The “Shockley diode equation” Io is the reverse saturation current V is the voltage across the junction Photodiodes—Current-Voltage Characteristics: Photocurrent generated by irradianceEe(W/m2) Photocurrent generated by optical power ϕe (W) Dr. Mike Nofziger 2014 Lecture 12

  7. Photodiodes—Current-Voltage Characteristics: Dr. Mike Nofziger 2014 Lecture 12

  8. Photodiodes—Use in an Electrical Circuit: Operated at V = 0 “zero-bias”: Output is very linear over 7-decades of flux Operated at –V “reverse-bias”: Capacitance decreases, speed increases Operated at I≈0 “open-circuit”: The open-circuit voltage is logarithmic with flux: NOT the preferred way to operate a photodiode! Dr. Mike Nofziger 2014 Lecture 12

  9. Basics of Solar Cells:● A solar cell is a Photovoltaic (“PV”) detector: - is made of Silicon (not silicone!!) - absorbs light from ≈ 350nm – 1100nm - the absorption of light “frees up” electrons - This creates a voltage at the terminals of the cell (the “Open-Circuit” voltage)- If the cell’s terminals are shorted, the maximum current will flow (the “Short-Circuit” current)- If a load resistor is connected to the cell, a current will flow (the “Photocurrent”) Dr. Mike Nofziger 2014 Lecture 12

  10. Basics of Solar Cells:● The Power (Watts) that the cell can produce is given by:● Because of internal resistance in the cell, the maximum power you can generate is across a load resistance equal to the internal resistance.www.keithley.com Dr. Mike Nofziger 2014 Lecture 12

  11. “Sources of Light” • LED – Light Emitting Diode • – solid-state, semiconductor p-n junction • – GaAs, AlGaAs, GaP, AlGaInP, GaN, InGaN,etc. • – 3mm, 5mm, or 8mm dia. plastic packages • Low-Power LED’s • 1-20mA of electrical current • “on/off indicators” • High-power LED’s •  500mA to >1A • Lumileds, Osram, Cree • Lighting!! • Replace incandescent bulbs Dr. Mike Nofziger 2014 Lecture 12

  12. “Sources of Light” • LED – Light Emitting Diode Dr. Mike Nofziger 2014 Lecture 12

  13. “Sources of Light” • White-Light LED’s: General Approaches Reference Dr. Mike Nofziger 2014 Lecture 12

  14. “Sources of Light” • White-Light LED’s (3 phosphors, “tri-phosphor”) • – AlGaInN LED is the source of light • – emits light in the near-UV spectral region • – 380-430 nm • – 3 phosphor coatings on top • – Europium-based red and blue phosphors • – Copper and aluminum doped zinc sulfide • green phosphor • – Color-mixing more easily controlled to produce • a pure white light. • – Example: CREE Reference Dr. Mike Nofziger 2014 Lecture 12

  15. “Sources of Light” • White-Light LED’s (1 phosphor) • – GaN semiconductor LED is the source of light • – emits blue light 450 – 470 nm • – Yellow phosphor coating on top • – Cerium-doped YAG: Y3Al5O12:Ce3+ • – light is emitted by scintillation (no afterglow) Example: CREE Dr. Mike Nofziger 2014 Lecture 12

  16. “Sources of Light” • White-Light LED’s: TRENDS Reference Reference Dr. Mike Nofziger 2014 Lecture 12

  17. “Sources of Light” • White-Light LED’s: Applications vs. Dr. Mike Nofziger 2014 Lecture 12

  18. “Sources of Light” • White-Light LED’s: Applications Uses a CREE XM-L 1000 lumen LED Dr. Mike Nofziger 2014 Lecture 12

  19. Laser Diodes—LI Curve Dr. Mike Nofziger 2014 Lecture 12

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