Correlation of film morphology and defect content with the charge-carrier transport in thin-film transistors based on ZnO nanoparticles

Abstract

The correlation of defect content and film morphology with the charge-carrier transport in field-effect devices based on zinc oxide nanoparticles was investigated. Changes in the defect content and the morphology were realized by annealing and sintering of the nanoparticle thin films. Temperature-dependent electrical measurements reveal that the carrier transport is thermally activated for both the unsintered and sintered thin films. Reduced energetic barrier heights between the particles have been determined after sintering. Additionally, the energetic barrier heights between the particles can be reduced by increasing the drain-to-source voltage and the gate-to-source voltage. The changes in the barrier height are discussed with respect to information obtained by scanning electron microscopy and photoluminescence measurements. It is found that a reduction of surface states and a lower roughness at the interface between the particle layer and the gate dielectric lead to lower barrier heights. Both surface termination and layer morphology at the interface affect the barrier height and thus are the main criteria for mobility improvement and device optimization

Atomic-layer-deposition-assisted ZnO nanoparticles for oxide charge-trap memory thin-film transistors

“…These stretched-out phenomenon in the C-V curves for the as-fabricated device was more remarkable when the measurement frequency increased from 10 kHz to 1 MHz, even though the considerable degree of frequency dispersions was generally detected for the metal-semiconductor-insulator structures using the oxide semiconductors owing to themoderate value of electron mobility [38]. Furthermore, if a large number of undesirable trap sites were located in the interfaces within the gate stack and a considerable amount of surface states also existed on the ZnO NP surfaces [39,40], the trap/de-trap process as well as the depletion-to-accumulation transition could be markedly delayed especially in a high-frequency regime. Consequently, these results clearly indicate that the annealing process performed at appropriate conditions can be a good solution to improve the interface quality within the gate stack and enhance the memory device characteristics of the fabricated NP-MTFTs.…”

Low-temperature solution-processed zinc oxide field effect transistor by blending zinc hydroxide and zinc oxide nanoparticle in aqueous solutions

“…However, previous ZnO nanoparticle transistor results from other groups showed that the electrical performance could be improved by increasing the crystallites size, of which the latter was acquired from the AFM or scanning electron microscope (SEM). 15,16,25) Thus, the ZnO nanoparticle films were likely formed through the Vollmer-Weber growth mechanism, where the crystallites boundary could limit the charge conduction. The AFM images show that the ZnO film formed by the proposed method contains relatively larger ZnO crystallites compared to the ZnO film formed by Zn(OH) 2 and ZnO 1 H 2 O.…”

“…If the general doping effect is not present, the large crystallite size decreases the number of the boundary over which the electron can pass, resulting in increase in mobility. 15,16) Thus, the observation of relatively larger ZnO crystallite size on the ZnO film formed by the blending approach could be the possible factor for the improvements in electrical performance. The ZnO films were further characterized using XPS.…”

“…3) A ZnO film could have a larger grain size with lesser ion impurities by increasing the post-annealing temperature. 15,16) However, this is not a desirable method of improving the ZnO film characteristics because the main advantage of the carbon-free aqueous solution approach is that it enables the metal oxide film to be formed at low process temperatures. Thus, improving the ZnO film characteristics without increasing the annealing temperature is necessary to enhance the electrical performance of a ZnO transistor.…”