The effects of thickness on the electrical, optical, structural and morphological properties of Al and Ga co-doped ZnO films grown by linear facing target sputtering

We investigated the effects of thickness on the electrical, optical, structural, and morphological properties of Al and Ga co-doped ZnO films (AGZO) grown by linear facing target sputtering (LFTS) for use as a transparent contact layer (TCL) in GaN-light emitting diodes (LEDs). Below a critical thickness of 200 nm, the resistivity and optical transmittance of the AGZO films were significantly affected by the thickness of the AGZO films. However, above a thickness of 200 nm, the AGZO films had similar resistivities and optical transmittances due to the stable columnar structure, which developed at a thickness of 200 nm. Due to the change of the growth mode with increasing thickness, the microstructure and surface morphology were also affected by the film thickness. Based on the figure of merit values, we determined that the optimized thickness of the LFTS-grown AGZO film was 200 nm, which was applied in a GaN-LED as a TCL. Successful operation of GaN-LEDs with an optimized AGZO film without plasma damage indicates that the LFTS-grown AGZO film is promising plasma damage-free TCL for use in GaN-LEDs.