Ultraviolet light-emitting diode arrays using Ga-doped ZnO as current spreading layer

Abstract

In this article, the authors investigate the fabrication and characterization of the 4 × 4 GaN-based ultraviolet (UV) light-emitting diode (LED) array with a pixel size of 200 × 200 μm2 and a pitch of 200 μm. For comparison, the single broad-area LED with a size of 400 × 400 μm2 is also fabricated from the same epitaxial wafer as a reference. The Ga-doped ZnO (GZO) film is used as a current spreading layer onto the ultraviolet LEDs to enhance the light output power. The GZO film with a thickness of 100 nm was deposited by atomic layer deposition (ALD) and has an electron concentration of ∼8 × 1020 cm−3, a low resistivity of ∼4 × 10−4 Ω cm, and a high transmittance of ∼84% in the near UV wavelength range. The ALD-GZO film was also used as the internal wires to connect the pixels of an LED array. The LEDs have a peak wavelength of 370 nm with a slight redshift at higher injection currents. The 4 × 4 LED array has a better performance in the maximum light output power density of 7.25 W/cm2 at 240 mA and a highly linear light output power to injection current, while the broad-area LED only exhibits the maximum light output power density of 1.34 W/cm2 at 70 mA. The single pixel of a 4 × 4 UV LED array reveals a maximum light output power density of 7.25 W/cm2 at 240 mA and a wider divergence angle of 137°, which are better than the broad-area LED of 1.34 W/cm2 at 70 mA and 128°, respectively. Finally, the authors show the demonstration of photos of an 8 × 8 LED array.