Structural Properties of Thin ZnO Films Deposited by ALD under O-Rich and Zn-Rich Growth Conditions and Their Relationship with Electrical Parameters

Abstract

The structural, optical, and electrical properties of ZnO are intimately intertwined. In the present work, the structural and transport properties of 100 nm thick polycrystalline ZnO films obtained by atomic layer deposition (ALD) at a growth temperature (Tg) of 100–300 °C were investigated. The electrical properties of the films showed a dependence on the substrate (a-Al2O3 or Si (100)) and a high sensitivity to Tg, related to the deviation of the film stoichiometry as demonstrated by the RT-Hall effect. The average crystallite size increased from 20–30 nm for as grown samples to 80–100 nm after rapid thermal annealing, which affects carrier scattering. The ZnO layers deposited on silicon showed lower strain and dislocation density than on sapphire at the same Tg. The calculated half crystallite size (D/2) was higher than the Debye length (LD) for all as grown and annealed ZnO films, except for annealed ZnO/Si films grown within the ALD window (100–200 °C), indicating different homogeneity of charge carrier distribution for annealed ZnO/Si and ZnO/a-Al2O3 layers. For as grown films the hydrogen impurity concentration detected via secondary ion mass spectrometry (SIMS) was 1021 cm−3 and was decreased by two orders of magnitude after annealing, accompanied by a decrease in Urbach energy in the ZnO/a-Al2O3 layers.

Substantial lifetime enhancement for Si-based photoanodes enabled by amorphous TiO2 coating with improved stoichiometry

“…While this study suggested a low-temperature crystalline-free amorphous film is preferable for achieving a long lifetime, the unreacted precursor ligands and byproducts were another inevitable issues associated with the low-temperature ALD processes. These impurities could substantially change the film properties, such as electronic and ionic transport properties, mechanical stability, and chemical reactivity 21 – 24 , which may open another pathway to breaking the current protection lifetime limit. In this paper, we report a fundamental discovery of the detrimental role of the residual Cl ligand in amorphous TiO 2 films to the PEC protection lifetime.…”

Cathodoluminescent Imaging of ZnO:N Films: Study of Annealing Processes Leading to Enhanced Acceptor Luminescence

“…We have used integral width in the Debye–Scherrer model [ 20 ] instead of FWHM of diffraction peaks to get more accurate crystallite size. Analysis of XRD data using the Debye–Scherrer model reveals average crystallite size increases from ≈100 to 200 nm for ZnO/HR‐Si after successive RTP treatment temperature from 400 °C to 800 °C ( Figure ), which is in accordance with results reported for undoped ZnO films.…”

“…Analysis of XRD data using the Debye–Scherrer model reveals average crystallite size increases from ≈100 to 200 nm for ZnO/HR‐Si after successive RTP treatment temperature from 400 °C to 800 °C ( Figure ), which is in accordance with results reported for undoped ZnO films. [ 20 ] This may be explained by accounting coalescence for small crystallite domains thermally produced by diffusion at their boundaries, resulting in increased crystallite growth. [ 21 ] The transfer of atoms at grain boundaries from one crystallite to another is the process of crystallite development, and the ultimate crystallite size is determined by the annealing conditions.…”

“…The mobility of charge carriers is regulated by the polycrystalline crystallite size; therefore, crystallite size is a key structural characteristic of thin films. [20][21][22] It can be calculated as…”

Multimodal X-ray probe station at 9C beamline of Pohang Light Source-II

“…5(c). The lattice mismatch strain is relaxed by generating dislocations that are strongly correlated with the electrical conductance behavior (Moon et al, 2012;Mishra et al, 2021). It is noteworthy that the as-grown ZnO thin film is in a compressive state compared with the bulk c-lattice constant of 5.213 A ˚.…”