Highly Conducting and Very Thin ZnO:Al Films with ZnO Buffer Layer Fabricated by Solid Phase Crystallization from Amorphous Phase

Abstract

We propose a novel method of oxide crystal growth via atomic-additive mediated amorphization. By utilizing this method, solid-phase crystallization (SPC) of ZnO from amorphous phase has been successfully demonstrated via nitrogen atom mediation. The resultant SPC-ZnO films are highly orientated and the crystallinity is higher than that of the films prepared by conventional sputtering. By using the SPC-ZnO as a buffer layer, the resistivity of ZnO:Al (AZO) films is drastically decreased. 20 nm-thick AZO films with a resistivity of 5  10-4  cm and an optical transmittance higher than 80% in a wide wavelength range of 400-2500 nm have been obtained.

Model for thickness dependence of mobility and concentration in highly conductive zinc oxide

“…[11][12][13][14][15][16][17] However, it must be remembered that ρ and n (but not μ) require knowledge of the electrical thickness d el , which may not be the same as d. That is, the Hall effect does not directly measure a volume concentration n ðcm −3 Þ, but a sheet concentration n s ðcm −2 Þ. If n is uniform, then these two quantities are simply related by n ¼ n s ∕d el , where d el ¼ d − δd is the electrical thickness, the region that contains free electrons.…”

“…[5][6][7][8][9][10] The attractiveness of ZnO in these applications is partially due to the demonstrations of high-quality growth on many different substrates using many different growth techniques. However, a troubling problem is that films on lattice-mismatched substrates nearly always exhibit a thickness dependence of the electrical parameters, resistivity ρ, mobility μ, and carrier concentration n. [11][12][13][14][15][16][17] The origin of this problem seems to be connected with poor crystallinity near the substrate/layer interface. Recently, however, Itagaki et al 16,18,19 have demonstrated significant improvement in the crystallinity of radio frequency (RF)-sputtered ZnO by inserting a thin ZnON buffer layer between the substrate and ZnO layer.…”

“…However, a troubling problem is that films on lattice-mismatched substrates nearly always exhibit a thickness dependence of the electrical parameters, resistivity ρ, mobility μ, and carrier concentration n. [11][12][13][14][15][16][17] The origin of this problem seems to be connected with poor crystallinity near the substrate/layer interface. Recently, however, Itagaki et al 16,18,19 have demonstrated significant improvement in the crystallinity of radio frequency (RF)-sputtered ZnO by inserting a thin ZnON buffer layer between the substrate and ZnO layer. For example, in undoped ZnO grown on c-plane aluminum oxide (Al 2 O 3 ), the rocking-curve full width half maximum of the (002) diffraction drops from 0.490 to 0.061 deg, and in Al-doped ZnO (AZO) grown on quartz-glass substrates, the thickness dependences of ρ, μ, and n greatly decrease.…”

Contrasting transparent conductive properties of ZnO films on amorphous and crystalline substrates in view of thickness dependence

“…4 The ultimate level of performance is achieved if columnar texture domains grow just from the interface. 2 Another approach is covering a glass substrate with a ZnO buffer layer [5][6][7] so that it acts a virtual template for pseudoepitaxial growth. The subsequently deposited conductive film has superior crystallinity.…”

ZnO:Al Thin Films with Buffer Layers Fabricated via Nitrogen Mediated Crystallization: Effects of N₂/Ar Gas Flow Rate Ratio

“…Recently, we have developed a novel fabrication method of sputtered ZnO films utilizing nitrogen-atom mediated crystallization (NMC) [7,8]. The ZnO films have well aligned crystal orientation and higher crystallinity than the films prepared by a conventional sputtering because the nucleation density can be reduced by using the NMC method.…”