Optimization of the emission characteristics of light emitting diodes by surface plasmons and surface waveguide modes

In this letter, the influence of metal films and dielectric waveguides on t he radiation characteristics of light emitting diodes (LEDs) is investigate d. Cross and hexagonal surface grating structures are used to excite surfac e plasmons and waveguide modes in these media. A beam divergence as small a s 17 degrees is achieved for a hexagonal grating coated with a 40 nm Ag fil m. The maximum quantum efficiency is found for a hexagonal grating with a 1 0-nm-thick Au film and a 250-nm-thick dielectric layer. The optical power e mitted by this LED into the solid angle from -30 degrees to 30 degrees is 1 0% higher than that of an LED without metal film and dielectric layer. (C) 2000 American Institute of Physics. [S0003- 6951(00)04941-X].