Effects of Nitrogen on Crystal Growth of Sputter-Deposited ZnO Films for Transparent Conducting Oxide

Abstract

We have studied the effects of the N2 gas flow rate on the surface morphology of ZnO films deposited by the sputtering of a ZnO target using Ar/N2. Height-height correlation function (HHCF) analysis indicates that introducing a small amount of N2 (<5 sccm) to the sputtering atmosphere enhances adatom migration, leading to a larger grain size in the ZnO films associated with an increase in the lateral correlation length. The HHCF analysis also reveals that films deposited with and without N2 exhibit a self-affine fractal surface structure. We demonstrate that utilizing such ZnO films deposited using Ar/N2 as buffer layers, the crystallinity of ZnO:Al (AZO) films on the buffer layers can be greatly improved. The electrical resistivity of 100-nm-thick AZO films decreases from 1.8×10-3 to 4.0×10-4 Ω·cm by utilizing a ZnO buffer layers prepared at N2 flow rate of 5 sccm.

Effects of morphology of buffer layers on ZnO/sapphire heteroepitaxial growth by RF magnetron sputtering

“…Figure 6 shows full width at half maximum (FWHM) of the (0002) symmetric rocking curves for ZnO films on NMC-ZnO buffer layers as a function of T s during the buffer layer deposition. Here, all the ZnO films are epitaxially grown on c-sapphire substrates, where the epitaxial relationship between ZnO and sapphire is [0001] ZnO ||[0001] sapphire and ZnO || [11][12][13][14][15][16][17][18][19][20] sapphire . ZnO films with high out-of-plane alignment are obtained by using NMC buffer layers fabricated at T s =700-760 o C. While, on the buffer layer fabricated at T s =780 o C, ZnO film shows large FWHM of 0.26 o .…”

“…However, because of the low crystallization temperature of ZnO, it is difficult to obtain amorphous like layers by just lowering the deposition temperature. Recently, we have developed a new type of buffer layers fabricated by "nitrogen mediated crystallization (NMC) method", where nucleation and crystal growth is controlled by not lowering deposition temperature, but introducing impurity atoms that inhibit crystal growth [10][11][12][13]. By utilizing the buffer layers fabricated by NMC method (NMC-ZnO buffer layers), we have succeeded in fabrication of atomically-flat ZnO films on lattice mismatched sapphire substrates.…”

Morphology Evolution Of ZnO Thin Films Deposited By Nitrogen Mediated Crystallization Method

“…The Ar/N2 flow rate ratios were 24.5/0, 19.5/5, 18.5/6, and 8.5/16 sccm. The detailed experiment was discussed elsewhere [6]. 2D Power Spectral Density Analysis and Height Distribution Analysis were derived from AFM measurement using Veeco Nanoscope II.…”

“…Nitrogen flow rate control during the deposition has been reported to be one of keys in determining the physical and chemical properties of the films. The introduction small amount of nitrogen during the fabrication of the buffer layer have remarkably improved the surface roughness and increased the grain size of the film and hence leading to the improvement of crytallinity, morphology, and electrical properties of AZO films [6]. Nonetheless, the detail morphological evolution of the ZnO buffer layers due to the nitrogen addition has not yet been fully understood.…”

Off-axis sputter deposition of ZnO films on c-sapphire substrates by utilizing nitrogen-mediated crystallization method

“…[18][19][20][21][22] During epitaxial growth of ZnO films on unbuffered c-plane sapphire substrates, highly strained two-dimensional (2-D) layers are initially formed due to the large lattice mismatch between ZnO and sapphire. On the 2-D layers, subsequent growth of three-dimensional (3-D) columnar grains with poor alignment occurs so that the strain energy stored in the film is released (Stranski-Krastanov mode).…”