Ferromagnetic Behavior and Magneto-Optical Properties of Semiconducting Co-Doped ZnO

Abstract

ZnO is a well-known semiconducting material showing a wide bandgap and an n-type intrinsic behavior of high interest in applications such as transparent electronics, piezoelectricity, optoelectronics, and photovoltaics. This semiconductor becomes even more attractive when doped with a few atomic percent of a transition metal. Indeed, e.g., the introduction of substitutional Co atoms in ZnO (ZCO) induces the appearance of room temperature ferromagnetism (RT-FM) and magneto-optical effects, making this material one of the most important representatives of so-called dilute magnetic semiconductors (DMSs). In the present review, we discuss the magnetic and magneto-optical properties of Co-doped ZnO thin films by considering also the significant improvements in the properties induced by post-growth irradiation with atomic hydrogen. We also show how all of these properties can be accounted for by a theoretical model based on the formation of Co-VO (oxygen vacancy) complexes and the concurrent presence of shallow donor defects, thus giving a sound support to this model to explain the RT-FM in ZCO DMSs.

Sensitivity Enhancement of CO2 Sensors at Room Temperature Based on the CZO Nanorod Architecture

“…51 For CZO-75W, the observed decrease in the n carriers can be accounted for by the Zn vacancies (V Zn ), which can induce the acceptor level, while oxygen vacancies behave as deep donors and Zn as shallow donors. 52 Gas-Sensing Properties of the CZO Sensors. Figure 7 depicts the resistance-time change reaction of the CZO sensors when exposed to CO 2 gas ranging from 1 to 1500 ppm at room temperature under dry air.…”

“…In addition, the inhibitory effect of such doping on the production of O 2 -derived defects at the ZnO grain boundary surfaces is the possible reason for the decrease of resistivity that occurred after the introduction of Co dopant into the ZnO matrix . For CZO-75W, the observed decrease in the n carriers can be accounted for by the Zn vacancies (V Zn ), which can induce the acceptor level, while oxygen vacancies behave as deep donors and Zn as shallow donors …”

Particles–Matrix Bond in ZnCoO:H and ZnCoAlO:H Films: Issues of Magnetism and Spin Injection

“…Zinc oxide is characterized as a wide-gap (~3.3 eV) semiconductor in which free carriers coexist with optical transparency [ 3 , 4 ]. At the same time, ZnO diluted with metal ions R (ZnRO) can be characterized by a high magnetic moment at room temperature [ 5 , 6 , 7 ]. However, the nature of the magnetism in such materials is still under debate.…”

“…In recent years, the hydrogenation of ZnCoO films has become increasingly popular. It has been established that the preparation or post-synthesis treatment of the films in a hydrogen atmosphere induces or enhances the ferromagnetism of the samples [ 7 , 15 , 16 , 17 , 18 , 19 , 20 ]. Hydrogen injection into ZnCoO was usually carried out by post-irradiation with a hydrogen ion beam [ 7 ], post-synthesis plasma treatment with Ar-H 2 mixed gas [ 19 , 20 ], post-synthesis annealing in H 2 or Ar/H 2 atmosphere [ 16 , 17 ], and radio frequency (RF) magnetron sputtering in Ar-H 2 mixed gas [ 15 , 18 ].…”

“…It has been established that the preparation or post-synthesis treatment of the films in a hydrogen atmosphere induces or enhances the ferromagnetism of the samples [ 7 , 15 , 16 , 17 , 18 , 19 , 20 ]. Hydrogen injection into ZnCoO was usually carried out by post-irradiation with a hydrogen ion beam [ 7 ], post-synthesis plasma treatment with Ar-H 2 mixed gas [ 19 , 20 ], post-synthesis annealing in H 2 or Ar/H 2 atmosphere [ 16 , 17 ], and radio frequency (RF) magnetron sputtering in Ar-H 2 mixed gas [ 15 , 18 ]. At the same time, it has been shown that the temperature during the hydrogenation of samples plays a key role in the formation of their physical properties [ 21 , 22 ].…”