High-efficiency vertical AlGaInP light-emitting diodes with conductive omni-directional reflectors

In order to increase extraction efficiency of AlGaInP-based vertical red light-emitting diodes (LEDs), AlGaInP LEDs employing a conductive omni-directional reflector (ODR) using transparent conducting oxide (TCO)/Ag is presented. The ODR consisted of p-type GaP, TCO layer (ITO, IZO, or AZO), and an Ag layer. The transmittance of the ITO, IZO, and AZO films were found 96%, 95%, and 91% after annealing at 350 degrees C at the wavelength of 620 nm, respectively. Forward voltages of the LEDs with TCO/Ag were slightly higher than that of the LED with Ag due to the high resistivity of the TCO. However, the brightness of the AlGaInP LEDs with ODR using ITO, IZO, and AZO measured at 20 mA increased significantly by 42%, 38%, and 29% compared with that of the LED with Ag reflector. (C) 2011 Elsevier B.V. All rights reserved.