Role of hafnium doping concentration on the structural and surface properties of ZnO surfaces

Abstract

The presented thesis deals with the characterisation of hafnium doped zinc oxides with focus on the application as transparent conducting film (TCF) or electron transport layer (ETL) in heterojunction solar cells. Atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electrical and optical methods have been applied to characterise the examined samples with the focus on AFM. Different AFM techniques are presented, conducted on some training samples and finally applied to investigate the evolution of the Hamaker constant in dependence of hafnium doping concentrations in zinc oxide. The thin film samples with a thickness of 75 nm were grown by atomic layer deposition and varying cycle ratios of diethyl-zinc and tetrakisethylmethylaminohafnium were used to control the doping concentrations. It has been shown that the Hamaker constant increases with doping concentration and peaks for a 1:1 cycle ratio and decreases at higher doping concentrations. The same trend has been observed for band gap, carrier concentration and force of adhesion. The reliability of retrieving Hamaker constants via the relatively new method of bimodal imaging method in comparison to using reconstructed force curves is presented. The observed high heterogeneity of the samples is assumed to be caused by polycrystallinity. High-resolution transmission electron microscopy (HRTEM) was able to confirm the polycrystallinity of the samples.