BRAGG REFLECTOR OF GAALAS/ALAS LAYERS WITH WIDE BANDWIDTH APPLICABLE TO LIGHT-EMITTING-DIODES

Reflective spectra of the Bragg reflectors applied to GaAs infrared light emitting diodes were simulated. Bragg reflectors are composed of alternating Al0.2Ga0.8As/AlAs layers where the ratio of high- and low-refractive indices is as small as 1.16. The reflectance bandwidth can be broadened by employing chirped structures where the optical thicknesses of the respective layers are changed arithmetically. On the other hand, for chirped Bragg reflectors, resonant reflection drops appeared at some wavelengths. These drops can be corrected by inserting periodic alternating layers. The reflectance band of 80% reflectivity is 2.7 times as wide as that of the conventional reflector of the periodic sequence in the case of 66 layer stack.