Transparent conductive aluminium and fluorine co-doped zinc oxide films via aerosol assisted chemical vapour deposition

Abstract

Aerosol assisted chemical vapour deposition (AACVD) was employed to synthesise highly transparent and conductive ZnO, fluorine or aluminium doped and aluminiumfluorine co-doped ZnO thin films on glass substrates at 450 o C. All films were characterised by X-ray diffraction (XRD), wavelength dispersive X-ray spectroscopy (WDX), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and UV/Vis/Near IR spectroscopy. The films were 300-350 nm thick, crystalline and displayed high transparency at 550 nm (80-90%). The co-doped film consisted of 1 at.% fluorine and 2 at.% aluminium, exhibiting a charge carrier concentration and a charge carrier mobility of 3.47 x 10 20 cm -3 and 9.7 cm 2 V -1 s -1 , respectively. The band gap of the co-doped film was found to be 3.7 eV and the plasma edge crossover was ca. 1800 nm. This film had a highly structured morphology in comparison to the un-doped and single doped ZnO films for transparent conducting oxide applications.

Transparent conducting n-type ZnO:Sc – synthesis, optoelectronic properties and theoretical insight

“…From the pure ZnO micrograph it is apparent that the ZnO is growing in a platelet-like morphology, similar to that observed in ZnO:Al films grown via AACVD in previous study. 71 As Sc loading increases, this morphology is retained by the ZnO crystallites though there is the distinct appearance of a secondary phase forming at the fringes of the ZnO. As well as having been predicted by our model (see eqn (3)), previous studies suggest that this is probably the amorphous secondary phase Sc 2 O 3 , which grows in competition with the doped ZnO:Sc phase.…”

“…suggests that such defects are likewise preferentially formed under an oxygen-poor deposition environment, which helps to rationalise the trend that lower resistivities are observed in nominally undoped ZnO films deposited from the oxygen-poor diethyl zinc precursor ([Zn(CH 2 CH 3 ) 2 ]), 71 when compared with those obtained from the zinc acetate precursor ([Zn(OCOCH 3 ) 2 ]), which is richer in oxygen, in the present work. It should be noted that overall, we consider the deposition environment used in the present study to be largely oxygen-poor, having been carried out under inert gas with the only sources of oxygen for oxide formation being the molecular acetate precursors and in the solvents present.…”

“…The cause for the initial increase in mobility is unclear, though previous ZnO:Al doping study has noted an increase in the carrier mean free path at low dopant levels, in spite of a shrinking crystallite diameter relative to the undoped material. 79 The ionised impurity scattering is typically the dominant scattering mechanism at higher dopant levels (n = 10 It is also interesting to note that those nominally undoped ZnO films, deposited also via AACVD but from a diethyl zinc precursor as opposed to the zinc acetate precursor used here, exhibit low resistivities similar to those measured for Al-doped ZnO in the same study (r ZnO E r ZnO:Al = 2.2 Â 10 À3 O cm), 71 while undoped ZnO deposited here from zinc acetate has r = 1. (002) and (101) peaks.…”

“…The Zn 2p 3/2 peak occurred at 1021.3 eV at low doping levels, agreeing with the 1021.5 eV obtained for ZnO thin films deposited via AACVD in previous studies. 71 This blue-shifted slightly to 1021.4 eV for films with bulk Sc doping over 1 at% relative to Zn (as determined by EDX). Zn(II) and Sc(III) were revealed as being the only oxidation states present, with no occurrence of metallic Zn(0) or Sc(0).…”

Investigation of characteristics of ZnO:Ga nanocrystalline thin films with varying dopant content

“…In order to examine the effect of Ga on ZnO, these solutions were mixed in different molar ratios ranging from 0% to 6% with step of 2%. In the light of other studies [22,23], it can be said that over-doping is undesirable because it leads to deterioration in the film structure. Thus, the mobility of the free electrons is reduced.…”