Structural and Electrical Properties of Atomic Layer Deposited Al‐Doped ZnO Films

Abstract

Structural and electrical properties of Al‐doped ZnO (AZO) films deposited by atomic layer deposition (ALD) are investigated to study the extrinsic doping mechanism of a transparent conducting oxide. ALD‐AZO films exhibit a unique layer‐by‐layer structure consisting of a ZnO matrix and Al2O3 dopant layers, as determined by transmission electron microscopy analysis. In these layered AZO films, a single Al2O3 dopant layer deposited during one ALD cycle could provide ≈4.5 × 1013 cm−2 free electrons to the ZnO. The effective field model for doping is suggested to explain the decrease in the carrier concentration of ALD‐AZO films when the interval between the Al2O3 layers is reduced to less than ≈2.6 nm (>3.4 at% Al). By correlating the electrical and structural properties, an extrinsic doping mechanism of ALD‐AZO films is proposed in which the incorporated Al atoms take oxygen from the ZnO matrix and form doubly charged donors, such as oxygen vacancies or zinc interstitials.

Structural, optical, electrical and resistive switching properties of ZnO thin films deposited by thermal and plasma-enhanced atomic layer deposition

“…Low carrier concentration and low conductivity (high resistivity) are observed for samples grown at lower temperature, and they increase with increasing the temperature up to 200 • C, and then decrease with further increasing the temperature to 300 • C. The samples grown at 200 • C show the highest carrier concentration of ∼7.7 × 10 19 cm −3 and the highest electron mobility of ∼13.6 cm 2 /V s, resulting in a high conductivity of 169 S/cm (resistivity: 0.0059 cm) without intentional doping. Although the high conductivity of the Thermal ALD grown ZnO films is not good for the fabrication of resistive switching devices as shown later, it is good for other applications such as transparent conducting films and high conductive layer [21]. On the other hand, the PEALD grown ZnO films showed resistivities much higher than 10 4 cm, unable to be measured electrically.…”

Workfunction of Al-Doped ZnO Films Deposited by Atomic Layer Deposition

“…al. 17 under similar ALD conditions. In contrast to this reference, however, no minimum in resistivity was found within this dopant range, and the general trend showed a more slightly decreasing resistivity with increasing Al doping levels, regardless of deposition geometry (Figure 3).…”

Nano-Material and Structural Engineering for Thermal Highways

“…The development of ALD-grown TCO materials was started by KPI's group concerning an investigation of electron transport behavior and charge generation mechanism of Al-doped ZnO (AZO) as a replacement of the most popular indiumtin-oxide (ITO) [14,15]. The precedent studies performed by KPI's group have mostly focused on structural and electrical characterization of ALD-AZO films.…”