Abstract
We report on the fabrication of Al-doped ZnO (AZO) transparent-conductive oxide (TCO) films on glass substrates by RF- sputtering, their physical properties, and the effect of thermal annealing on the AZO TCO films. The AZO films on glass substrates have a preferred orientation of the c-axis, irrespective of deposition conditions, which means that the AZO films have textured structures along the c-axis. The film thickness and surface roughness in the AZO films are proportional to plasma power and deposition time, while they are inverse-proportional to working gas ratio and working pressure. The AZO films have the optical transmittance over 80 % in the wavelength range of 400 - 1000 nm, irrespective of deposition conditions. The plasma power and the deposition time relatively give a large influence on the optical transmittance, compared to the working gas ratio and the working pressure. The AZO films deposited at room temperature have poor electrical properties, while the thermal annealing under Ar ambient significantly improves the electrical conductivity of the AZO films: an as-deposited sample has an electrical resistivity of 87 Wcm and an electron concentration of 1.3´10 17 cm -3 , while the annealed sample has an electrical resistivity of 3.7´10 -2 Wcm and an electron concentration of 1.2´10 20 cm -3 .
Highlights
Transparent conductive oxide (TCO) has attracted strong attention as the unprecedented applications such as smart phone, tablet PC, and flat panel display, etc beyond the existing devices such as solar cell and LED come on stage one after another [13]
The electron concentration approaches to the level of low 1021 cm-3 and the electrical resistivity approaches to the level of low 10-4 Wcm in the Al-doped ZnO, Ga-doped ZnO, and Indoped ZnO films, fabricated by pulsed-laser deposition (PLD), metal-ogranic chemicalvapor deposition (MOCVD), atomic-layer deposition (ALD), DC sputter, and RF sputter [6,7,8,9,10]
Al-doped ZnO is very powerful and effective when used in the target sources of sputters, because the sputtering system has the merits of low cost, massproductivity, and convenient maintenance, compared to other thin film fabrication systems such as PLD, MOCVD, and ALD
Summary
Transparent conductive oxide (TCO) has attracted strong attention as the unprecedented applications such as smart phone, tablet PC, and flat panel display, etc beyond the existing devices such as solar cell and LED come on stage one after another [13]. AZO, Al-doped ZnO has been studied as a promising material for transparent conductive oxides (TCOs) for a long time due to the wide bandgap of 3.37 eV and the high n-type conductivity by native donor-type defects [1,2,3]. The inappropriate fabrication conditions of the low growth temperature that is not enough to supply the formation energy of ZnO bonds and the heterosubstrate with a large lattice mismatch of ZnO unit cells, are known to generate the various donor-type native defects unintentionally, though the background electron concentration level of the ZnO films depends on their growth techniques [4,5]. Al-doped ZnO is very powerful and effective when used in the target sources of sputters, because the sputtering system has the merits of low cost, massproductivity, and convenient maintenance, compared to other thin film fabrication systems such as PLD, MOCVD, and ALD. We report on the fabrication process of AZO TCO films on glass substrates by RF-sputtering, their physical properties such as surface, structural, optical, and electrical properties, and influence of thermal annealing on the electrical properties of AZO TCO films
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