Lecture19

Lecture19

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: well-structure blue and violet light-emitting diodes,” Appl. Phys. Lett 67, 1868 (1995). Georgia Tech •The shape of the “die” (chip) can greatly aid light extraction by minimizing internal reflections ECE 3080 - Dr. Alan Doolittle EE 332 Spring 2013 Homojunction LED Design Considerations Homojunction LED Design Considerations Homojunction LED Design Considerations Electron Current P-type GaP P-type GaP O Electron Current O F FNN -qVA A -qV FPFP Light Light Zn Zn N-type GaP N-type GaP Hole Current Hole Current •Efficient light generation results from Donor-Acceptor pair transition requires high •Efficient light generation results from Donor-Acceptor pair transition – – requires high doping level so Donor and acceptor are “close to each other”. doping level so Donor and acceptor are “close to each other”. Georgia Tech E3080 - Dr. Alan Doolittle ECE E 332 Spring 2013 How to HowWhite LEDs White Make to Make Georgia Tech Slide Credit to Dr. Oliver Brandt, Ga Tech LEDs? EE 332 Spring 2013 ECE 3080 - Dr. Alan Doolittle Spontaneous Light Emission Light Material Interaction • • • • We can add to our understanding of absorption and spontaneous radiation due to random recombination another form of radiation – Stimulated emission. Stimulated emission can occur when we have a “population inversion”, i.e. when we have injected so many minority carriers that in some regions there are more “excited carriers” (electrons) than “ground state” carriers (holes). Given an incident photon of the bandgap energy, a second photon will be “stimulated” by the first photon resulting in two photons with the same energy (wavelength) and phase. This phase coherence results in minimal divergence of the optical beam resulting in a directed light source. EE 332 Spring 2013 Spontaneous vs Stimulated Light Emission Emission Spontaneous vs Stimulated Light Emission The power-current curve of a laser diode. Below threshold, the diode is anan LED. Above threshold, the The power-current curve of a las...
View Full Document

This document was uploaded on 02/18/2014.

Ask a homework question - tutors are online