Dissertation > Industrial Technology > General industrial technology > Materials science and engineering > Special structural materials

Studies on Structures and Properties of Doped Ge-Sb-Se Thin Films Sensitive to Fe~(3+)、Cd~(2+) Ions

Author ZhangHaiFang
Tutor DuZuoYi
School Zhejiang University
Course Materials Science
Keywords Ge-Sb-Se Fe/Ni doping CdS doping thin film low-temperature sintered ion sensitive
CLC TB383.2
Type Master's thesis
Year 2006
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Ge-Sb-Se chalcogenide glass is a famous ion sensitive material system. It can be used for detecting and monitoring metal ion content in food industry, environment protection, and industry process and so on when metal elements were doped, with advantages of high stability and high corrosion resistance. It has properties of armorphous semicondutor and owns high compatibility with the IC technology. The preparation of thin films is on agenda along with the micromation of apparatus. However, nowadays, the preparation technology of ion sensitive thin films was complex and of high cost, with not so many successful preparation technology applied in practical thin film apparatus; Researchers pay less attention on doped Ge-Sb-Se thin films which used as Fe ion or Cd ion sensitive materials; Tthe properties should be enhanced and well controlled for the application of thin films apparatus. And metal elements doping, including the species, contents and process, shows strong relation with the charge transfer, which is one essencial pricipal in ion sensitive process. Thus, it is of high importance to develop a simple preparation technology of thin films for ion sensitive materials and to investigate the doped Ge-Sb-Se ion sensitive materials for the realization of useful thin films apparatus.In this essay, Fe, Ni doped Fe2.5-xNix(Ge28Sb17Se55)97.5 (x=0, 2.5) thin films were grown by electron-beam evaporation with targets sintered at low temperature. These thin films showed p-typed in conducting status. The results suggested thin films had a more perfect network and less defects if ion doped has a higher activity and smaller electronegative difference with the system elements or films had been annealed. Fe and Ni doped in Ge-Sb-Se system did not only take part in binding and affect the network perfection but also introduced defects near Fermi energy. Compared with thin films doped with Fe, Thin films doped with Ni had a more perfect network, lower neutron-hanging binding concentration and less polarons produced under AC electric field compared with Fe doped thin films, thus had a smaller roughness, larger optical band gap, higher carrier mobility, lower carrier concentration and smaller dielectric loss. A faster interface kinetic process and a higher sensitivity to Fe3+ ion were obtained in iron doped thin films. With a tendency of crystallization, thin films annealed showed a narrower band edge tails, and behaved a faster interface kinetic process due to the increased driving force of electron by the enhanced built-in electric field in the interface.In this essay, we also prepared CdS doped Ge-Sb-Se thin films by electro-beam evaporation with low-temperature sintered targets (CdS)x(Ge28Sbi2Se6o)ioo-x(x=O> 2> 4^ 7), as well as CdS doped Ge-Sb-Se thin films under different substrate temperature with low-temperature sintered targets (CdS)4(Ge28Sbi7Se55)96. The Cd contents in thin films can be controlled and the Ge/Sb/Se ratio in thin films of the substrate temperature changes series is close to 28/12/60. The results suggested the Cd in thin film do not only take part in high-energy bonding but also exist as defect site, thus thin films doped with CdS showed larger optical band gap, less band edge tails and lower resistivity, this trends went on as the CdS doping content increased.The structure and properties of CdS doped Ge-Sb-Se thin films varied with the substrate temperature. The diffusion ability and the desorption velocity of atoms was both affected by the substrate temperature for the energy provided. Under the opposite effect of the increasing of the diffusion ability and the increasing of desorption velocity, the network perfection of the thin films first increased and then decreased while the defects state in the thin films behaved the oppisite trends, thus the width of band edge tails, the dielectric loss and the plane resistivity of the thin films first increased and then decreased, as well as the optical band gap showing the reverse, the thin films behaved the least band edge tails, the lowest dielectric loss, the largest optical band gap and the lowest plane resistivity when the network perfection was the highest. A crystallization trends were arised when the diffusion abilitiy was too high. These thin films all showed Cd2+ ion sensitivities. In low acidity, thin films prepared with substrate temperature of 100°C and 150°C showed the highest linearity in the Cd2+ concerntration ranged from 10’6-10"’mol/L, and behaved the stable Cd2+ ion sensitivities of 7-8mV/Dec.

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