AVS 52nd International Symposium
    Electronic Materials and Processing Monday Sessions
       Session EM+NS-MoM

Paper EM+NS-MoM4
Quantitative Assessment of Diffusivity and Specularity of Textured Surfaces for Light Extraction in Light-Emitting Diodes

Monday, October 31, 2005, 9:20 am, Room 310

Session: Novel Approaches in Wide Bandgap Semiconductors
Presenter: Y.A. Xi, The Future Chips Constellation
Authors: Y.A. Xi, The Future Chips Constellation
X. Li, The Future Chips Constellation
J.K. Kim, The Future Chips Constellation
F. Mont, The Future Chips Constellation
Th. Gessmann, The Future Chips Constellation
H. Luo, The Future Chips Constellation
E.F. Schubert, The Future Chips Constellation
Correspondent: Click to Email
Light extraction in GaN-based light-emitting diodes (LEDs) is limited by the large difference of the refractive index between GaN and the ambient material. The texturing of surfaces and interfaces can improve the light-extraction efficiency into the surrounding medium. Surface-textured reflectors fabricated by natural lithography and ion-beam etching are shown to have a specular as well as a diffusive component of the reflectivity. The diffusely reflected power and the specularly reflected power of surface-textured reflectors are measured and analyzed quantitatively in terms of a new theoretical model. The diffusivity, that is diffusive-power-to-total-power ratio, is determined and shown to strongly depend on the surface texture. Diffusivities of 38.1% and 42.8 % are obtained for the reflectors masked with 445 nm and 740 nm nano-polystyrene balls, respectively, much higher than the 0.35 % of a planar Silver reflector. The light-extraction efficiency from a waveguide, clad by a partially diffuse reflector, is analyzed and shown to be enhanced. In addition, the spatial transmittance pattern of the textured surface is also measured and analyzed by using the same theoretical model. Our study shows that this model can be used to quantitatively assess the dependence of the light-extraction efficiency on the diffusivity of textured surfaces in GaN-based LEDs.