Electronic transition and electrical transport properties of delafossite CuCr1−xMgxO2 (0 ≤ x ≤ 12%) films prepared by the sol-gel method: A composition dependence study

Abstract

Highly transparent CuCr1−xMgxO2 (0 ≤ x ≤ 12%) films were prepared on (001) sapphire substrates by sol-gel method. The microstructure, phonon modes, optical band gap, and electrical transport properties have been systematically discussed. It was found that Mg-doping improved the crystal quality and enhanced the (00l) preferred orientation. The spectral transmittance of films approaches about 70%–75% in the visible-near-infrared wavelength region. With increasing Mg-composition, the optical band gap first declines and climbs up due to the band gap renormalization and Burstein-Moss effect. The direct and indirect band gaps of CuCr0.94Mg0.06O2 film are 3.00 and 2.56 eV, respectively. In addition, it shows a crossover from the thermal activation behavior to that of three-dimensional variable range hopping from temperature-dependent electrical conductivity. The crossover temperature decreases with increasing Mg-doping composition, which can be ascribed to the change of spin-charge coupling between the hole and the local spin at Cr site. It should be noted that the electrical conductivity of CuCr1−xMgxO2 films becomes larger with increasing x value. The highest electrical conductivity of 3.85 S cm−1 at room temperature for x = 12% is four-order magnitude larger than that (8.81 × 10−4 S cm−1) for pure CuCrO2 film. The high spectral transmittance and larger conductivity indicate that Mg-doped CuCrO2 films are promising for optoelectronic device applications.

A review on the p-type transparent Cu–Cr–O delafossite materials

“…For example, both direct and indirect band gaps are influenced by the content of Mg within the Mg/ CuCrO 2 . They decrease for concentrations of Mg up to 8% but an increasing is then observed for greater dopant content [181]. This was attributed to the band gap renormalization and Burstein-Moss effect induced by the dopant.…”

“…In order to accelerate the synthesis, Kumar et al use the microwave heating, as it enhances solid-state reaction kinetics [178]. Another chemical method of fabrication for copper chromium delafossite is the sol-gel process [179][180][181][182][183][184][185][186]. Copper and chromium hydrate precursors are dissolved in alcoholic or water-based solutions.…”

“…The significant span for the band gap's values is again a result of the diversity of deposition methods and post-treatments. These band gaps might be tailored by tuning the deposition parameters [214] or the level of doping [181,220]. For example, both direct and indirect band gaps are influenced by the content of Mg within the Mg/ CuCrO 2 .…”

Temperature-dependent band gap, interband transitions, and exciton formation in transparentp-type delafossiteCuCr1−xMgLi1, Han2, Zhang3 et al. 2014Phys. Rev. B172120View full textAdd to dashboardCite

“…More important reason is that the overdoping Mg disturbs the up-spin Cr 3d orbitals, which greatly impedes the dispersion of the 3d states [10]. The less disperse electronic states decrease the effective transport and holds back the increase of the conductivity.…”

“…In our previous work, the sol-gel derived CuCr 1−x Mg x O 2 films have been proved to possess relatively high transmittance above 70% in the visible-near-infrared wavelength region. It has been found that the conductivity of CuCr 1−x Mg x O 2 increases with the temperature from 150 to 300 K. There is a transition of the carrier transport mechanism from a thermal activation behavior to a variable range hopping at a certain temperature [3,10]. Nevertheless, the origins of absorption behavior and electrical transport properties have not been clarified to date.…”