Lembit Pung

University of Tartu, Dorpat, Tartu County, Estonia

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Publications (4)8.41 Total impact

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    ABSTRACT: HfO2 films were atomic layer deposited from HfCl4 and H2O on Si(100) in the temperature range of 300–600 °C. At low temperatures, films grow faster and are structurally more disordered, compared to films grown at high temperatures. At high temperatures, the films are better crystallized, but grow slower and contain grain boundaries extending from substrate to gate electrode. Film growth rate and capacitance of HfO2 dielectric layers was improved by depositing stacked structures with polycrystalline films of higher purity at 600 °C on thin HfO2 sublayer grown on Si at 300 °C.
    Thin Solid Films 05/2005; 479(1-2-479):1-11. DOI:10.1016/j.tsf.2004.11.191 · 1.76 Impact Factor
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    Jaan Aarik · Hugo Mändar · Marco Kirm · Lembit Pung
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    ABSTRACT: Optical absorption and photoluminescence of amorphous and crystalline HfO2 thin films grown by atomic layer deposition from HfCl4 and H2O were studied. Band-gap energy of (5.55±0.03) eV was determined for monoclinic HfO2 with mean crystallite sizes of 30–40 nm as well as for amorphous HfO2. Excitation in the range of intrinsic absorption resulted in emission that had maximum intensity at 3.2 eV in the case of amorphous films and at 2.6 or 4.4 eV in the case of monoclinic films. The emission intensity of crystalline films exceeded that of amorphous films by an order of magnitude at all temperatures studied. The main luminescence band at 4.4 eV was tentatively assigned to the emission of self-trapped excitons while the emission at lower photon energies was attributed to defects and impurities. With the increase of temperature from 10 to 295 K, the low-energy edges of excitation spectra shifted towards lower energies by 0.1 eV in the case of amorphous films and by 0.15 eV in the case of crystalline films, indicating corresponding changes in the band-gap energies.
    Thin Solid Films 11/2004; 466(1-2-466):41-47. DOI:10.1016/j.tsf.2004.01.110 · 1.76 Impact Factor
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    ABSTRACT: HfO2 films were atomic layer deposited from HfCl4 and H2O on Si(100) in the temperature range of 226–750 °C. The films consisted of dominantly the monoclinic polymorph. Elastic recoil detection analysis revealed high residual chlorine and hydrogen contents (2–5 at. %) in the films grown below 300–350 °C. The content of residual hydrogen and chlorine monotonously decreased with increasing growth temperature. The effective permittivity insignificantly depended on the growth temperature and water partial pressure. Capacitance-voltage curves exhibited marked hysteresis especially in the films grown at 400–450 °C, and demonstrated enhanced distortions likely due to the increased trap densities in the films grown at 700–750 °C. Changes in water pressure led to some changes in the extent of crystallization, but did not induce any clear changes in the capacitance of the dielectric layer.
    Journal of Applied Physics 10/2004; 96(9):5298-5307. DOI:10.1063/1.1796513 · 2.18 Impact Factor
  • Jaan Aarik · Kaupo Kukli · Aleks Aidla · Lembit Pung
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    ABSTRACT: In the present study, the possible surface processes during the atomic layer deposition (atomic layer epitaxy) of tantalum oxide thin films from TaCl5 and H2O were studied. Surface mass exchange was detected by means of quartz crystalline mass sensor (QCM) during the growth process. Using the results of QCM measurements and those of electron-probe composition analysis, and atomic ratios as well as stable surface concentration of Ta and Cl atoms in the intermediate surface layer were calculated versus growth temperature. The mechanisms of suboxide growth and etching in the continuous precursor flow was evaluated on the basis of the measurement results and thermodynamical probability for different reactions.
    Applied Surface Science 12/1996; 103(4):331-341. DOI:10.1016/S0169-4332(96)00554-5 · 2.71 Impact Factor