Chapter 5: LED basics: Optical properties (click on figure for full-size image)

Fig. 5.1. Parabolic electron and hole dispersion relations showing “vertical” electronhole recombination and photon emission. Fig. 5.2. Theoretical emission spectrum of an LED. The full width at half maximum (FWHM) of the emission line is 1.8 kT.
Fig. 5.3. (a) Definition of the escape cone by the critical angle Phi c . (b) Area element dA. (c) Area of calotte-shaped section of the sphere defined by radius r and angle Phi c. Fig. 5.4. Geometrical model used to derive the Lambertian emission pattern. (a) The light emitted into angle phi f inside the semiconductor is emitted into the angle d Phi in air. (b)Illustration of the area element dA of the calotte-shaped section of the sphere.
Fig. 5.5. Light-emitting diodes with (a) planar, (b) hemispherical, and (c) parabolic surfaces. (d) Far-field patterns of the different types of LEDs. Fig. 5.6. (a) LED without and (b) with dome-shaped epoxy encapsulant. A larger escape angle is obtained for the LED with an epoxy dome. (c) Calculated ratio of light extraction efficiency emitted through the top surface of a planar LED with and without an epoxy dome.
Fig. 5.7. Characteristic temperature T1 of GaInN/GaN blue, GaInN/GaN green, and AlGaInP/GaAs red LEDs near room temperature (after data from Toyoda Gosei Corp., 2000).