ECE3080-L-11d-LEDs and Lasers

ECE3080-L-11d-LEDs and Lasers - Lecture 11d Light Emitting...

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ECE 3080 - Dr. Alan Doolittle Georgia Tech Lecture 11d Light Emitting Diodes and Laser Diodes Reading: (Cont’d) Notes and Anderson 2 Chapter 11.3-11.4.5 Some images from Anderson and Anderson text
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ECE 3080 - Dr. Alan Doolittle Georgia Tech Some semiconductor materials and their wavelength ranges. Based on data from References 3 to 5. Optical Design Choices
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ECE 3080 - Dr. Alan Doolittle Georgia Tech P-n Junction I-V Characteristics Electron Diffusion Current Electron Drift Current Hole Diffusion Current Hole Drift Current In Equilibrium, the Total current balances due to the sum of the individual components
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ECE 3080 - Dr. Alan Doolittle Georgia Tech Electron Diffusion Current Electron Drift Current Hole Diffusion Current Hole Drift Current Current flow is proportional to e (Va/Vref) due to the exponential decay of carriers into the majority carrier bands Review: p-n Junction I-V Characteristics Current flow is dominated by majority carriers flowing across the junction and becoming minority carriers QuickTime Movie
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ECE 3080 - Dr. Alan Doolittle Georgia Tech Electron Diffusion Current negligible due to large energy barrier Electron Drift Current Hole Diffusion Current negligible due to large energy barrier Hole Drift Current Current flow is constant due to thermally generated carriers swept out by E- fields in the depletion region Current flow is dominated by minority carriers flowing across the junction and becoming majority carriers QuickTime Movie Review: p-n Junction I-V Characteristics
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ECE 3080 - Dr. Alan Doolittle Georgia Tech Where does the reverse bias current come from? Generation near the depletion region edges “replenishes” the current source. Review: p-n Junction I-V Characteristics
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ECE 3080 - Dr. Alan Doolittle Georgia Tech Review: p-n Junction I-V Characteristics Putting it all together Reverse Bias: Current flow is constant due to thermally generated carriers swept out by E-fields in the depletion region Forward Bias: Current flow is proportional to e (Va/Vref) due to the exponential decay of carriers into the majority carrier bands Current flow is zero at no applied voltage I=I o (e Va/Vref -1)
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ECE 3080 - Dr. Alan Doolittle Georgia Tech Light Emitting Devices – Basics Emission of photons by recombination of electrons and holes in direct bandgap materials Photoluminescense : excess electrons and holes required for the radiative recombination are generated by photon absorption Electroluminescense : excess electrons and holes required for the radiative recombination are result of an electrical current www.osram.com Slide Credit to Dr. Oliver Brandt, Ga Tech
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ECE 3080 - Dr. Alan Doolittle Georgia Tech LED Applications LED Displays LED Brake Lights LED Head Lights LED Text Slide Credit to Dr. Oliver Brandt, Ga Tech
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Georgia Tech … and at Georgia Tech? Slide credited to Dr. Oliver Brandt, Ga Tech
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ECE3080-L-11d-LEDs and Lasers - Lecture 11d Light Emitting...

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