Abstract
In recent years, gallium-doped zinc oxide (GZO) has passed into a very popular material as transparent conductive oxide (TCO) films to apply on InGaN-based light-emitting diodes (LEDs). GZO is a wide band-gap and n-type semiconducting oxide, which can be used as a transparent contact. The results reveal that the atomic layer deposition (ALD)-GZO films with a thickness of 250 nm have an electron concentration of ~1 × 1021 cm-3, low resistivity of ~4 × 10-4 Ω-cm, and high transmittance (~90%) at the visible wavelengths. In order to enhance the transmittance in short wavelengths of GZO films, we employed Zn and Mg driven-in ALD-GZO films via the novel method of rapid-thermal diffusion. The ultraviolet-visible spectrum shows a significant blue-shift of the absorption band edge and an increasing optical band gap for the Zn and Mg driven-in GZO films. Additionally, we used circular transmission line model (CTLM) to perform the experiment of Ni/Au ohmic contact on p-GaN, and tried to adjust the thickness of Ni and annealing temperature to obtain optimum Ni/Au ohmic contact on p-GaN. We acquired the best specific contact resistance (ρc) is 1.4 × 10-3 Ω•cm2. By means of Zn and Mg driven-in GZO as transparent conducting layer onto 400- and 380-nm InGaN/GaN, the electroluminescence intensity of 400- and 380-nm LEDs with Zn and Mg driven-in GZO films has nearly 1.4 and 2.5 times of magnitude stronger than the conventional LEDs only with GZO films at 20 mA. The 400- and 380-nm LEDs with Zn and Mg driven-in GZO films also reveal a light output power of 7.7 and 1.9 mW at 20 mA as compared to the conventional LEDs only with GZO films of 6.1 and 0.7 mW, respectively. The 400- and 380-nm LEDs also exhibit an enhancement of 27% and 166% in light output power. These results present that Zn and Mg driven-in ALD-GZO films have significant improvement for the light extraction on the shorter wavelengths for the violet and ultraviolet (UV) LEDs.