Thin film AlGaInP light emitting diodes with different reflectors

The reflectivity versus incident angle of a GaP/Au reflector,a GaP/SiO2/Au triple ODR (omni-directional reflector) and a GaP/ITO/Au triple ODR was calculated.Compared to AIGalnP LEDs with a GaAs absorbing substrate,thin film LEDs with a Au reflector,a SiO2 ODR and an ITO ODR were fabricated.At a current of 20 mA,the optical output power of four samples was respectively 1.04,1.14,2.53 and 2.15 m W.The Au diffusion in the annealing process reduces the reflectivity of the Au/GaP reflector to 9%.The different transmittance of quarter-wave thickness ITO and SiO2 induces different optical output power between the SiO2 and ITO thin film LEDs.The insertion of Zn in the ITO ODR LED does not affect the light output but evidently reduces the voltage.