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LABORATORY
SEMICONDUCTOR HETEROSTRUCTURS

HEAD: Assoc.Prof. Simeon Simeonov, Ph.D.
tel: 7144-228; e-mail: simeon@issp.bas.bg

TOTAL STAFF: 8
RESEARCH SCIENTISTS: 7

Assoc.Prof. S.Alexandrova, Ph.D.
Assoc.Prof. P.Danesh, Ph.D.
Assoc.Prof. A.Szekeres, Ph.D.
Assoc. Prof. S.Kaschieva, Dr.Sci.
Assoc.Prof. N.Peev, Ph.D.
E.Kafedjiiska, Research Scientist
A.Gushterov, Ph.D. student
T.Nikolova, Ph.D. student


RESEARCH ACTIVITIES:

1. THERMALLY GROWN ULTRA-THIN (<20nm), SiO2-Si and SiOxNy-Si STRUCTURES
    Electrically active defects have been characterized in ultra-thin (<20 nm) SiO2 films grown by to thermal oxidation of Si substrates subjected to H.F. hydrogen plasma treatment this characterization is carried out by an analysis of the frequency dependence of volt-capacitance characteristics measured in the frequency range of 100 Hz to 1MHz.

    By atomic force microscopy the surface morphology of hydrogenated Si substrates and thermally grown SiO2 films on then have been established.

    The structural of defects in SiO2 films have been investigated by I.R. spectroscopy and computer simulation of oxide structure. A correlation between defects and mechanical stress and roughness has been revealed.

    The hydrogen profiles in 60 nm SiO2 film on Si substrate after hydrogen ion bombardment with energy of 0.8 or 1.6 keV have been determined. It is shown that in accumulation mode electrical charge transfer is carried out by electron tunnelling via deep levels in SiO2 films. Such tunnelling current has been established also in 120nm SiO2/Si structures after 11 keV hydrogen ion implantation.

    By admittance (capacitance and parallel conductance) measurements of SiOxNy /Si structures it have been shown that a low temperature annealing decreases the concentration of O3 ≡ Si* and OH - defect centers.

    Spectral ellipsometrical investigations of thin SiO2 films prepared by plasma enhanced chemical vapour deposition (PECVD) to the Si substrate have shown that nitrogen addition to the plasma ambient leads to the deposition of silicon oxynitride films with different concentration of nitrogen. At certain conditions electrically active defects which contain non-oxidized silicon atoms, appear in deposited oxide films. These defects lead to the increase of the electrical current through the insulator films. Strong photoluminescence is observed in PECVD carbon films after a nitrogen addition to the plasma ambient during film deposition.

2. HIGH-ENERGY IRRADIATION OF SiO2-Si STRUCTURES

    Effects of high-energy electrons or gamma irradiation on the interface states of ion implanted MOS structures have been investigated by thermally stimulated charge (TSC) method. The n-type Si-SiO2 samples with oxide thickness of 20 nm, 200 nm and 300 nm are implanted with 50 keV boron ions to a dose of 1.5x1012 cm-2. Formed MOS structures are irradiated with 11 MeV electrons or 60Co γ-rays. The energy position and the concentration of the radiation-induced interface traps are determined. It is shown that the kinds of radiation-induced interface traps and their concentration depend on the position of the maximum of the previously implanted boron ions with respect to the Si-SiO2 interface.

    SiO2/Si structures implanted with Si+ ions and irradiated with high-energy electrons were studied by means of ultra soft X-ray emission spectroscopy with variations of the electron excitation energy. It was found that previous Si+ ion implantation blocks the oxidation of the Si-substrates irradiated with 20 MeV electrons. This effect is more pronounced for samples prepared on n-type silicon substrates, and it also depends on the post oxidation treatment of the samples.

    It was shown that preliminary high-energy electron irradiation for 10 seconds is an efficient way for decreasing the annealing temperature of radiation defects introduced by ion implantation. The recombination-enhanced-defect reaction mechanism as a possible explanation of the annealing temperature decrease is proposed.

3. HYDROGENATED AMORPHOUS SILICON

    A study of post-hydrogenation of magnetron sputtered amorphous silicon films has been carried out with the aim to elucidate the effect of hydrogen interaction with amorphous silicon network on its short and medium range order. Raman spectroscopy and nuclear reaction analysis (NRA) have been used to establish the variations in the amorphous structure and the amount and depth distribution of the penetrated hydrogen, respectively. The values of hydrogen concentration evaluated by NRA and infrared spectroscopy coincide within the measurement accuracy, suggesting that the hydrogen in-diffusion proceeds via interaction with the silicon atoms. This interaction is accompanied by a rearrangement of the strained Si-Si bonds which leads to an improvement of the amorphous network.


PUBLICATIONS:
  1. N.A.Hastas, C.A.Dimitriadis, J.Brini, G.Kamarinos, V.K.Gueorgiev, S.Kaschieva, Effects of gamma-ray irradiation on polycrystalline silicon thin-films transistors. Microelectronics Reliability 43, 57-60 (2003).
  2. S.Kaschieva, S.N.Dmitriev, Hr.Angelov, Electron beam and g-irradiation of ion implanted MOS structures with different oxide thickness. Nucl.Instr.Meth. in Phys.Res. B 206, 452-456 (2003).
  3. S. Kaschieva, An advantage of MOS structures with ultra thin oxide during irradiation. Material Science and Engineering B 100, 23-26 (2003)
  4. S.N. Shamin, V.R. Galakhov, S. Kaschieva, S.N.Dmitriev, A.G. Belov, Soft X-ray emission spectroscopy of the SiO2/Si structures irradiated with high-energy electrons. Journal of Material Science-Material in Electronics 14, 809-810 (2003)
  5. B. Pantchev, P. Danesh, K. Antonova, B. Schmidt, D. Grambole, J. Baran, "Effect of film thickness on hydrogen content in a-Si:H". Journal of Material Science: Materials in Electronics, vol.14, 751-752 (2003).
  6. P. Danesh, B. Pantchev, E. Liarokapis, B. Schmidt, "Raman study of ion-implanted hydrogenated amorphous silicon". Journal of Material Science: Materials in Electronics, vol.14, 753-754 (2003).
  7. P. Danesh, B. Pantchev, I. Savatinova, E. Liarokapis and B.Schmidt: Effect of ion implantation on the structural properties ofa-Si:H films, Vacuum, 69, 83-86 (2003).
  8. B. Pantchev, P.Danesh, U.Kreissig and B.Schmidt:Elastic recoil detection analysis of ion-exchanged soda-lime glass substrates for a-Si:H devices,Vacuum 69, 289-292 (2003).
  9. Gyorgy, I.N. Mihailescu, M. Baleva, M. Abrashev, E.P. Trifonova, A. Szekeres, A. Perrone, "Correlation between the chemical bonding and the physical properties of the CNx films obtained by pulsed laser deposition from C targets in low pressure N2" Materials Sci. Engineering B 37, 251-257 (2003).
  10. Gesheva KA, A. Szekeres, T. Ivanova, "Optical Properties of APCVD Thin Films of Molybdenum and Tungsten Based Metal Oxides". Solar Energy Mater. Solar Cells, 76, 563-576 (2003).
  11. A.Paneva, A. Szekeres, "Effect Of Rf Hydrogen Plasma Annealing On The Properties Of SiO2/Si Structures: A Spectroscopic Ellipsometry Study". Thin Solid Fims 433, 367- 370 (2003).
  12. R.E. Tanner, A. Szekeres, D. Gogova, K. Gesheva,"Studies on the CVD-WO3 thin films surface by atomic force microscopy and spectroscopic Ellipsometry" Materials Sci. - Materials in Electronics, 14, 769-770 (2003).
  13. S. Simeonov, S. Gushterov, E. Kafedjiiska, A. Szekeres, "Trap-assisted tunneling in p-Si/SiO2 structures" J. Materials Sci. - Materials in Electronics, 14, 801-802 (2003).
  14. V. Pamukchieva, A. Szekeres, K. Todorova, "Optical study of GexSb20-xTe80 chalcogenide films" J. Materials Sci. - Materials in Electronics, 14, 837-838 (2003).
  15. R.E. Tanner, A. Szekeres, D. Gogova, K. Gesheva, "Study of the surface roughness of CVD-tungsten oxide films". Appl. Surf. Sci, 218, 162-168 (2003).
  16. С.Касчиева, С.Н.Дмитриев, Взаимодействие МЭВ электронов с МОП структурами. Взаимодействие излучений с твердом телом "Материалы пятой международной конференции" Минск, Беларусь, 2003, pp.162-164
  17. V.Pamukchieva, A. Szekeres, K. Todorova, "Photo-Induced Changes Of The Optical Constants Of Chalcodenide Ge19Sb1Te80 Films ". ROMOPTO 2003, Proceedings of SPIE
  18. E.Halova, S L'Universite.Alexandrova, A. Szekeres, M. Modreanu, "Silicon Oxynitride As Advanced Material For The Semiconductor Electronics: Electrical Characteristics" Annuaire de de Sofia, Faculte de Chimie
  19. S.Kaschieva, S.N.Dmitriev, W.Skorupa, Reduction of the annealing temperature of radiation-induced defects in ion implanted MOS structures. Appl.Phys. A 78 607-611 (2004)
  20. B.Pantchev, P.Danesh, E.Liarokapis, B.Schmidt, J.Schmidt and D.Grambole: Effect of post-hydrogenation on the structural properties of amorphous silicon network, Jap.J.Appl.Phys. , 43, (2004)
  21. P. Danesh, B.Pantchev, K.Antonova, E.Liarokapis, B.Schmidt, D.Grambole and J.Baran: Hydrogen bonding and structural order in hydrogenated amorphous silicon prepared with hydrogendiluted silane, J. Phys. D: Applied Physics, 37, 249 (2004)

ONGOING RESEARCH PROJECTS:

Financed by the Bulgarian Academy of Sciences
  1. "Structure and defects in micro and nano-sized heterostructures"

TEACHING ACTIVITIES:

Technical University, FDIBA, Lectures "General Physics", 300 hours


COLLABORATION:
  1. "Study of dopant redistribution in ion implanted semiconductor heterostructures after high-energy electron irradiation", with JINR, Dubna, Russia
  2. "Electrophysical and optical properties of CNx-Si,WCx-Si, AlNx-Si, SiCx-Si and
    BNx-Si heterostructures", with Institute of Atomic Physics, RA, Bucharest, Romania.
  3. "Optical and electrical properties of semitransparent metal layers on semiconductors" with Institute of Semiconductor Physics, NASU, Kyiv, Ukraine.
  4. "Investigation of structure, structure stress and properties of thin dielectric - silicon structures for micro and nano electronics", with Institute of Semiconductor Physics, NASU, Kyiv, Ukraine
  5. "Preparation and investigation of thin oxide layers and semiconductors for microelectronics and optoelectronics", with Institute of Physical Chemistry, RA, Bucharest, Romania.
  6. "Interaction of defects generated by ion implantation and other high energy irradiations in Si/SiO2 structures" with Rossendorf Research Centre, Germany.
  7. "Second Harmonics Generation in thin semiconductor and optoelectronics heterostructures", with RAS, Moskva, Russia
  8. "Investigation of semiconductor structures", with Institute of Metal Physics, RAS, Ekaterinbourg, Russia
  9. "Investigation of defects in semiconductor structures with double irradiation", with Institute of Semiconductor Physics, NASU, Kyiv, Ukraine

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