Carrier Concentration Of Thin Films Research Articles

Effect of lack of oxygen on optical and electrical properties of RF magnetron sputtering deposited CuFeO2−x thin films

Delafossite CuFeO[Formula: see text] thin films were fabricated on quartz substrate using radio-frequency sputtering deposition under low O2 flow ratios from 9% to 0% at room temperature. The as-deposited films were in amorphous phase and crystallized into rhombohedral 3R (R3m) delafossite structure after post annealing at 900[Formula: see text]C for 2 h in flowing N2 atmosphere. SEM images showed that the films were composed of nano-sized crystallized grains, thin film composed of smoother surface and higher oxygen content was obtained under higher oxygen percentage in sputtering gas. The optical transmission spectra of these films were studied in the wavelength range 200–1500 nm and the results revealed a narrowing trend of direct bandgap from 3.09 eV to 2.98 eV with the decrease of oxygen flow ratio during deposition. All of the post-annealed CuFeO[Formula: see text] thin films exhibited p-type conductivity and linear ohmic contact feature with Cu electrodes. The carrier concentration of thin films increased from [Formula: see text] to [Formula: see text] whereas the carrier mobility decreased from [Formula: see text] to [Formula: see text] as the oxygen flow ratio reduced from 9% to 0%. The ability of controlling compound composition enables tuning of carrier concentration and mobility in CuFeO[Formula: see text] and offering essential technical basis in engineering photoelectronic devices.

Optical and electrical responses of magnetron-sputtered amorphous Nb-doped TiO2 thin films annealed at low temperature

Nb-doped TiO2 (TNO) thin films were prepared by annealing at 300°C for 30min after a magnetron-sputter process. A laser-irradiated post-annealing Raman scattering analysis indirectly showed the possible formation of small size anatase TNO clusters within the thin film matrix Although the TNO thin films were not crystallized, oxygen vacancies were created by adding H2 into the sputter gas during the deposition process. This improved the conductivity and carrier concentration of the thin films. As the ratio of H2 in sputter gas is f(H2) = [H2/Ar+H2] = 10%, the carrier concentration of the amorphous TNO thin film reached 1022 (cm−3) with the resistivity being about 10−2 (Ω.cm). Even though a new methodology to decrease the fabrication temperature is not presented; this study demonstrates an efficient approach to shorten the annealing process, which ends prior to the crystallization of the thin films. Besides, in situ H2 addition into the sputter atmosphere is proven to be a good solution to enhance the electrical conductivity of semiconductor thin films like TNOs, despite the fact that they are not well crystallized.

BCS-to-BEC evolution details

Sá de Melo replies: I thank D. M. Eagles for his comments. My statement concerning the evolution from Bardeen-Cooper-Schrieffer to Bose–Einstein condensation superfluids was about clarity and not who was the first to propose the idea. Although I appreciate Eagles’s work, I still think that Anthony Leggett’s papers 1 are the clearest presentation on the topic up to 1980.In his very interesting book written in 1964, John Blatt describes the BEC theory of superconductivity and its relation to the BCS theory. 2 As he recounts, the possibility of pairing without superconductivity and Bose condensation of electron pairs at a lower temperature was suggested as early as 1946 by Richard Ogg Jr. In 1954 and subsequent years, Max Schafroth developed a firm theoretical framework for such pairing, but it was not supported by experimental evidence: No preformed pairs were found, and the BEC temperature was much too high for known superconductors. Blatt’s book thoroughly documents a clear connection between a variational, fixed-number ground state comprising antisymmetrized products of pair wavefunctions and the BCS equations that Eagles used in his 1969 paper. Eagles noticed that the BCS and number equations at zero temperature could be used to describe the evolution from BCS to BEC superconductivity in low-carrier-density thin films or bulk materials for fixed (and sufficiently strong) interaction and changing carrier density. However, Blatt’s main interest was in metals with high carrier densities. If one reads the full statement in the box entitled “Feshbach resonances” on page 47 of my article, it is clear that I am talking about changing interactions for fixed density and not changing density for fixed interactions. I do not think it is currently possible in any superconductor to control the interactions between fermions. Thus my statement is accurate.In many instances the change in carrier concentration in thin films or three-dimensional (bulk) systems is made via chemical doping, which may introduce disorder or distortions in the crystal structure and thus change the system in more than the desired way. I have serious doubts that ceramic samples of zirconium-doped strontium titanate described in Eagles’s letter indeed show the BCS-to-BEC evolution; the references provided do not offer clear evidence of such a phenomenon.Since cuprate superconductors are known to be quasi-2D and have d-wave pairing symmetry, the evolution from BCS to BEC superconductivity for sufficiently strong fixed interactions and changing carrier density would be accompanied by a topological quantum phase transition 3 and would not be a crossover as in the s-wave case. However, as much as I might want such a transition to be found for the cuprates, current experimental evidence shows that their normal state and superconducting properties are more complicated than simple BCS-to-BEC theories would predict.The beauty of the observation of the BCS-to-BEC evolution in ultracold atoms is that many of the materials difficulties encountered in standard condensed matter can be avoided and the tuning of the interaction for fixed low density can be controlled. However, one should keep an open mind that a similar realization may appear elsewhere. For instance, if carrier density could be controlled and changed continuously via electrostatic doping in good-quality thin films or at the surface of bulk low-carrier-density superconductors like some titanates or cuprates, then there is a good chance of observing the BCS-to-BEC evolution as a function of carrier density as envisioned by Eagles in 1969.REFERENCESSection:ChooseTop of pageREFERENCES << REFERENCES 1. A. J. Leggett, in Modern Trends in the Theory of Condensed Matter: Proceedings of the XVI Karpacz Winter School of Theoretical Physics, February 19-March 3, 1979, Karpacz, Poland, A. Pekalski, J. Przystawa, eds., Springer, New York (1980) Google Scholar A. J. Leggett, J. Phys. Colloq. 41, C7–19 (1980). https://doi.org/10.1051/jphyscol:1980704 , Google ScholarCrossref2. J. M. Blatt, Theory of Superconductivity, Academic Press, New York (1964). Google Scholar3. L. S. Borkowski, C. A. R. Sá de Melo, http://arxiv.org/abs/cond-mat/9810370v1 , Google Scholar R. D. Duncan, C. A. R. Sá de Melo, Phys. Rev. B 62, 9675 (2000). https://doi.org/10.1103/PhysRevB.62.9675 , Google ScholarCrossref, ISI© 2009 American Institute of Physics.

Effect of Ce doping on the growth of ZnO thin films

Recently, ZnO films doped by trivalent elements have attracted much attention for use in transparent conductive films. The impurity doping to control the carrier concentration generally causes degradation of crystallinity and preferred orientation which leads to the deterioration of electrical characteristics. In this paper, the effects of various doping trivalent elements on the growth process and change in carrier concentration in thin films are discussed. We find that the deteriorated crystallinity of ZnO film by Al doping is improved by Ce doping.

Precise measurements of oxygen content: Oxygen vacancies in transparent conducting indium oxide films

High precision electron probe microanalysis (EPMA) has been used to measure the correlation of oxygen deficiency with carrier concentration in thin films of amorphous indium oxide. This has shown that there are ten times as many oxygen vacancies as would be expected from the carrier concentration measurements, giving a doping efficiency of 0.1. It is therefore clear that the doping mechanism is more complex than the usual picture of every oxygen vacancy producing two free electrons.