Extrinsic Doping of Electrodeposited Zinc Oxide Films by Chlorine for Transparent Conductive Oxide Applications

Abstract

A systematic study of n-type zinc oxide thin films electrodeposition in presence of chloride ions is presented in this article. The incorporation of chlorine during the growth is characterized by several techniques, and its influence on the optoelectronic properties of the films is explored. Different deposition conditions have been tested; depending on the support electrolyte nature (nitrate or perchlorate) and on the chlorine concentration introduced in the bath, a large range of carrier concentrations has been reached (from 7.4 × 10 17 cm -3 for a nitrate electrolyte without chloride ions addition to 9 × 10 19 cm -3 in perchlorate conditions with a chloride concentration of 0.1 M). This evolution of the doping concentration evaluated by Mott-Schottky measurements and confirmed by Raman spectroscopy has a great effect on the optical transmission of the films. The increase in the doping concentration tends to shift the absorption edge to higher energies and to induces the decrease of the transmission in the near-infrared range because of the free carrier absorption. We finally propose a model to explain the effective n-type doping of ZnO with Cl, based on the intrinsic and extrinsic defects of the system.

Significant Carrier Concentration Changes in Native Electrodeposited ZnO

“…This range is in agreement with reported carrier concentrations for ZnO, 9,10 including ZnO electrodeposited from nitratebased electrolytes. 9,10 Our results indicate a higher n-type carrier concentration in ZnO that is electrodeposited at more positive deposition potentials. While some electrolytes, such as those containing Cl − or borane, 9,10 offer a clear opportunity for extrinsic doping, the same cannot be said for our nitratebased electrolyte.…”

“…In the context of traditional donor/acceptor band theory, a decreased band gap would indicate an increased carrier concentration, as has been observed recently with Cl-doped ZnO electrodeposits. 10 However, hydrogen doping in ZnO has been observed to go against this trend. 5,6 Hydrogen-donated electrons can fill empty states in the conduction band of ZnO when doping levels are high enough to create a degenerate semiconductor, thereby leading to increased band gaps with higher doping levels (Moss-Burstein effect).…”

Electrodeposition of nanoporous ZnO on Al-doped ZnO leading to a highly organized structure for integration in Dye Sensitized Solar Cells

“…These ZnO:Al layers were characterized by Hall effect and a doping level close to 5 × 10 20 cm −3 was found. This value can also be compared to that measured for a dense ZnO layer (3.65 eV) electrodeposited in very similar experimental conditions (chloride concentration, applied potential) which contains a doping concentration up to 10 20 cm −3 [36]. The shift of gap value could be related to the very high developed surface of the nanoporous ZnO that could lower the doping level of the material, but this aspect has to be investigated in more details.…”

EFFECT OF CHLORIDE IONS ON THE STRUCTURAL, OPTICAL, MORPHOLOGICAL, AND ELECTROCHEMICAL PROPERTIES OF Cu2O FILMS ELECTRODEPOSITED ON FLUORINE-DOPED TIN OXIDE SUBSTRATE FROM A DMSO SOLUTION

“…Thus, the Cu 2 O electrodeposition from DMSO-chloride solutions shows better performance than those that derive from DMSO-perchlorate solutions. The effect of chloride ions on the oxide semiconductor electrodeposition process has been previously studied in both aqueous 12,23 and DMSO solutions 22 . In reference to these studies, it is a well known fact, that chloride ions in aqueous solutions dope ZnO films during their electrodeposition 12 .…”

“…These films were p-type semiconductors with an optical band gap that varied between 2.18 eV -2.25 eV with a doping level between 8.2 x 10 18 cm -3 -2.0 x 10 19 cm -3 , depending on the electrodeposition temperature. On the other hand, it is a well known fact that during the electrodeposition process, the addition of complexing agents produces drastic changes in the morphology and properties of semiconductor materials [12][13] and metals [14][15] . This way, the influence of chloride ions as a complexing agent during the Cu 2 O electrodeposition process from a DMSO solution is analyzed in this article.…”