Light Emitting Diodes Outline - Luminescence Spectra of Atoms - LEDs. p-n Junction. Light Outcoupling - Organic LEDs - Quantum Dots in LEDs.

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Presentation transcript:

Light Emitting Diodes Outline - Luminescence Spectra of Atoms - LEDs. p-n Junction. Light Outcoupling - Organic LEDs - Quantum Dots in LEDs

“Characterization of Organic Illumination Systems” April 1, 1989, Hamburgen et al. Electrode #1 Penetration Electrode #2 Penetration Thermocouple Probe Device Under Test Electrode Separation Dimensions in inches Subject Electrode Orientation Electrode Separation Electrode #1 Penetration Electrode #2 Penetration Bok Choyparallel0.5 Mandarin Orangeparallel0.38 Cornichonaxial0.5 Kosher Pickleaxial Dill Pickleaxial Electrode Position:

p-n Junctions and LEDs High energy electrons (n-type) fall into low energy holes (p-type) p-typen-type Resistor Not Shown Resistor Power Source LED

p-n Junctions and LEDs ENERGY Small Gap Large Gap Yellow Light Emitted Red Light Emitted

ANODECATHODE Homojunction p-n Light Emitting Diode EgEg Forward Bias condition n p ECEC EVEV INJECTED ELECTRONS p-n Diode np “+” “−” ELECTRICITY IN  LIGHT OUT INJECTED HOLES EgEg Zero bias condition n p ECEC EVEV NO CHARGE INJECTED (NO LIGHT OUT) PHOTON EMITTED Diode Current Saturation Current in Reverse Bias Boltzman Constant Temperature Voltage Across Diode Forward Current CURRENT VOLTAGE VBVB Leakage Current Avalanche Current Breakdown Voltage Reverse Voltage

Extraction Efficiency of Planar LEDs critical angle of total internal reflection Problem: Only small fraction of light can escape from semiconductor. Above equation gives < 10% extraction efficiency for typical III-V. Trapped light ray High-index semiconductor Escape Cone

Artificial Lighting consumes 8% of US energy and 22% of US electricity The energy cost is estimated at $50B annually or $200 per capita Image in the Public Domain

INSTALLED EFFICIENCY FRACTION Incandescent 5% 12% Fluorescent20% 62% HID lamps25% 26% White LEDs35% ---- Note: Electric Motor Efficiency is 85%~90% All Images are in the Public Domain

Luminescence Efficiency [lm/W] Color Rendering Index Survey of Lightbulb Technology Performance (using data from bulbs.com) INCANDESCENT HALOGEN COMPACT FLUORESCENT QD VISION NEXXUS 110V LED CREE LR6 LED OTHER LED TECHNOLOGIES CREE LRP38 LED Tradeoff EFFICIENCY for COLOR QUALITY

OLED: The Green Display TV and PC Account for 1% each of US Electricity Usage Plasma LCD RPTV Power Usage [W/in 2 ] <0.05 OLED Plasma, LCD, RPTV power usage values from 2007 CNet report on commercial TV power consumption. OLED value projected from SID 2007 demo. US household power usage data from 2004 report by the Natural Resources Defense Council.

MIT OpenCourseWare Electromagnetic Energy: From Motors to Lasers Spring 2011 For information about citing these materials or our Terms of Use, visit: