Thickness study of AZO films by RF sputtering in Ar + H₂ atmosphere at room temperature

Abstract

Al‐doped ZnO (AZO) films were prepared on glass substrates by RF magnetron sputtering in an Ar + 5%H2 ambient at room temperature. The influence of film thickness (85–1101 nm) on the structural, electrical, and optical properties of the films was investigated. With increasing film thickness, it is found that the crystallinity of the films is improved and the surface roughness of the films increases. The decrease of resistivity is accompanied by an increase of carrier concentration and mobility. At the film thickness of 583–1101 nm, larger figures of merit (FOM) of the films can be obtained, in which the film with a thickness of 803 nm has the lowest resistivity of 3.13 × 10−4 Ω cm, a sheet resistance of 3.90 Ω/sq, and an average optical transmittance in the visible range of 80%. With increasing film thickness, the crystallite size, carrier concentration, and mobility of the films increase simultaneously, implying that the main scattering mechanism is the intercrystallite boundary scattering. It is found that the optical bandgap (Eg) increases from 3.50 to 3.72 eV with film thickness, and this increase can be ascribed to the Burstein–Moss (BM) effect after considering all possible effect factors. The results demonstrate that AZO films deposited in an Ar + H2 atmosphere at room temperature are suitable for application in thin‐film solar cells as transparent conductive electrode layers.

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.…”

Model for thickness dependence of mobility and concentration in highly conductive ZnO

“…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.…”

Structural and opto-electrical properties of Al doped ZnO sputtered thin films

“…The mostly used ZnO:Al thin film has been prepared with various methods: radio frequency (RF) sputtering [7], pulsed laser deposition [8], atomic layer deposition and chemical vapor deposition [9]. Many authors have studied the RF sputtering of ZnO:Al target [10][11][12][13]. Unfortunately, only few studies reported on doping by simultaneous magnetron co-sputtering techniques [14], the most important advantage of this method is the control of the charges carrier concentrations.…”

“…The films present good thermal stability, they are abundant, non toxic and not expensive [6]. The mostly used ZnO:Al thin film has been prepared with various methods: radio frequency (RF) sputtering [7], pulsed laser deposition [8], atomic layer deposition and chemical vapor deposition [9]. Many authors have studied the RF sputtering of ZnO:Al target [10][11][12][13].…”