Optoelectronic Devices Chapter 8 Solid State Electronic Devices, 6th Edition (Streetman and Banerjee)

ELEC 424

John Peeples

Optoelectronic Effect Photons of frequency 𝐸𝑔/ℎ add to generation current

The result is a family of reverse bias curves

•Photodiodes Solar Cells

Photodectectors

• Light Emitting Diodes

• Fiber Optics

• Lasers

Optoelectronic Devices

Photoconductivity Generation current disrupts equilibruim creating an open circuit voltage (Voc)

Realms of Operation No battery Reverse current

Solar Cells

Solar Cell Construction

Solar Cell “Fill Factor” • Maximum Power Figure of Merit • Voc – Bandgap Dependent • Isc – Area and Process Dependent

Notice that this is 4th Quadrant Operation (chart flipped around

for instructional purposes)

Solar Cell “Fill Factor”

• Maximum Power Figure of Merit • Voc – Bandgap Dependent • Isc – Area and Process Dependent

Ratio of this area

To this area

If Isc=100mA and Voc=0.8V, Then Pmax=(0.8)(100)(.7) =56mW if the fill factor is 70%.

Photodetectors • 3rd quadrant operation • P-Intrinsic-N • Impinging photons generate EHPs, changing Io • Ir reflects the shift in the 3rd quadrant characteristic

Light Emitting Diodes

• Brighter LEDs enable tailight and traffic light arrays

• Colors important for displays and for communications

Light Emitting Diodes

• LEDs operate in first quadrant (forward bias)

• Carriers injected across the junction must recombine

• Recombination in indirect band gap materials generates heat

Si

Ge

• Recombination in direct band gap materials generates light (and some heat)

GaAs

GaP Ternary and quaternary compounds

• Luminosity (brightness) and Color bands are important

Designer Light Emitters

• Energy varies near linearly with stoichiometry • Energy determines emitted frequency

• Stoichiometry dictates color

• Color dictates application

Red, Yellow, Green – traffic lights

Red, Blue, Green – color displays

Red – tail lights

IR, other non-visibles – communications

eV(eV)E

mnm

m)(1.24hchv(eV)E

g

red

g

82.168.0/24.1

68.0680

//

GaA0.68

P0.32

or Al0.32

Ga0.68

As

Electromagnetic Spectrum

Optical Fiber

• Greater capacity • Data rates of hundreds of Gbps

• Smaller size & weight

• Lower attenuation

• Electromagnetic isolation

• Greater repeater spacing • 10s of km at least

Optical Fiber - Benefits

• Long-haul trunks

• Metropolitan trunks

• Rural exchange trunks

• Subscriber loops

• LANs

Optical Fiber - Applications

• Act as wave guide for 1014 to 1015 Hz • Portions of infrared and visible spectrum

• Light Emitting Diode (LED) • Cheaper • Wider operating temp range • Last longer

• Injection Laser Diode (ILD) • More efficient • Greater data rate

• Wavelength Division Multiplexing

Optical Fiber Transmission Characteristics

Optical Fiber Transmission Modes

LightAmplification byStimulatedEmission ofRadiation

• Monochromatic • Coherent • Highly directional

Low to High IF

Homojunction Lasers

Heterojunction Lasers

•Photodiodes Solar Cells

Photodectectors

• Light Emitting Diodes

• Fiber Optics

• Lasers

Optoelectronic Devices