X-Ray diffraction and Raman spectroscopy for a better understanding of ZnO:Al growth process

Abstract

ZnO:Al thin films were prepared on glass substrates by radio frequency RF magnetron sputtering from a ceramic ZnO target mixed with Al2O3 (1 wt%) in pure argon atmosphere with a power of 250 W. Two series of samples were deposited, the first one as a function of the substrate temperature (between 20 and 325 • C) at 0.12 Pa, the second one as a function of the working pressure (between 0.01 and 2.2 Pa) at room temperature. The influence of these deposition parameters was studied by a detailed microstructural analysis using X-Ray diffraction and Raman spectroscopy. Their electrical properties were characterized by Hall effect measurements. As the substrate temperature is increased, crystallite size increases while the strain and the electrical resistivity decrease. An improvement of the crystallinity is deduced from Raman spectra and X-Ray diffraction patterns. From the pressure series, an electrical optimum is observed at 0.12 Pa. Above 0.12 Pa, there is a degradation of the crystallinity, attributed to the low mobility of the adatoms and below 0.12 Pa, high-energy sputtered particles damage the growing films. The trends given by Thornton structure zone model are also consistent with X-Ray diffraction results.

On performance limitations and property correlations of Al-doped ZnO deposited by radio-frequency sputtering

“…Here an interesting observation can be made. Most of the existing studies on sputtered AZO report an increase in grain size [7,49,9] and an increase in (001) texture coefficient [50] with decreasing resistivity, but inconsistent trends have been pointed out, especially for the case of RF sputtering [9,51,33]. From inspection of Fig.…”

“…Only very few works [33,34,35] have shown the root-mean square (RMS) micro-strain in AZO films. This quantity is fundamentally different from the (macroscopic) strain discussed in the previous section.…”

“…For this reason, we rely on SEM images in top view to visualize the in-plane grain size and we employ a standard data analysis procedure in XRD line profile analysis to deconvolute micro-strain and instrumental effects from the out-of-plane grain size [19]. Note that this method has been applied to AZO films in a very limited number of previous reports [33,34,35], with most studies not applying any kind of deconvolution. From the SEM images in top view (Fig.…”

Effect of annealing on silicon heterojunction solar cells with textured ZnO:Al as transparent conductive oxide

“…But because of its lower conductivity compared to ITO, (2 × 10 −3 Ω cm for ZnO:Al and 5 × 10 −4 Ω cm for ITO [8][9][10][11][12]), thick layers (1−2 µm) are required to achieve low series resistance in the device. Properties of this material can be found elsewhere [13].…”

High-efficiency plasma treatment for surface modification of LPCVD ZnO

“…Despite the fact that the shape of the presented spectra is strongly affected by scattering from glass substrate resulting in a broad band with the maximum around 460 cm -1 , it is obvious that spectra are similar for both samples. Two major vibrational modes observed in the spectra are the high frequency E 2 mode associated with vibration of oxygen atoms and A 1 LO mode [6].The intensity, position and width of the lines for both modes is approximately the same for both samples indicating no changes of crystallinity after 5 minutes plasma treatment.…”