Optoelectronics related to GaN-based semiconductors (i.e., InGaN, GaN, and AlGaN) are new technologies that have the potential to far exceed the energy efficiencies of incandescent and fluorescent lighting sources. Among the GaN-based optoelectronic devices like light emitting diode (LED) and laser diode (LD), the GaN-based LEDs are of interest for the next generation illumination because of the representative characteristics such as small, highly radiant, reliably long, and fast responding, compared with the existing general lighting systems.
Achievement of high luminous intensity by flip-chip LED (FCLED) with Ag-metallic reflector or using top emitting LED (TELED) with highly transparent ITO contact is required to improve the external quantum efficiency (EQE) and light output of GaN-based LEDs. However, since the work function of Ag and ITO is lower than 5.0 eV, it is difficult to produce low-resistance p-ohmic electrode with Ag-metallic reflector or ITO only.
In this study, in order to develop new ohmic contact materials having low contact resistance and high transmittance, transparent nanoparticles-embedded p-ohmic electrode, Mg-doped indium oxide (MIO) (3 nm)/indium tin oxide (ITO) (400 nm) ohmic contact for high brightness TELEDs for solid-state lighting, was suggested. The MIO/ITO contact become ohmic with specific contact resistances of 2.64 × 10-3 Ωcm2 and give transmittance higher than 94.6 % at a wavelength of 450 nm when annealed at 630 °C for 1 min in air. GaN-based LEDs fabricated with the annealed MIO/ITO p-contact layer give a forward-bias voltage of about 3.38 V at injection current of 20 mA. It is further shown that the output power of the LEDs with the MIO/ITO contact is enhanced by about 1.86 times at 20 mA as compared with that of LEDs with the conventional Ni/Au contact.