Photoconductive detection of vibronic states at semiconductor interfaces and thin films
Final Report Abstract
The main results of the project can be summarized as follows. Photoconductive method has been proposed and applied to investigate vibrational spectra of defects in semiconductors, whereby vibrational transitions appear in photoconductivity spectra as Fano resonances. With this approach interstitial hydrogen acting as donor in ZnO and rutile TiO2 was investigated. In particular, it was concluded that ionization energy of interstitial hydrogen in rutile is less than 300 meV, which is at variance with the recent theoretical calculations predicting a deep donor behavior. A combined photoconductivity and IR absorption study of the interstitial hydrogen donor in ZnO is presented. With the help of this probe system it was shown that sign, intensity, and shape of Fano resonances due to vibrational excitations of shallow donors occurring in the photoconductivity spectra strongly depend on the sample thickness and the presence of other electrically active impurities. The distortion of the "natural" Fano shape of the resonances for bulk samples is explained by the competing processes of photoionization and absorption at the frequency of the corresponding local vibrational mode. A quantitative model explaining all experimental results is proposed. Combined photoconductivity and IR absorption spectroscopy was applied to study hydrogen-related defects in single-crystalline SnO2. Our results strongly indicate that a defect with a stretch O-H vibrational mode at 3272 cm^-1 is a shallow donor with an ionization energy less than 300 meV. The defect is stable upon annealing up to ~450 °C and thus can be in part responsible for the persistent n-type conductivity of SnO2. The method of photoconductive detection of defects in semiconductor thin films was applied on commercial silicon-on-insulator wafers. It was shown that the method is suitable to probe shallow impurities as well as electrically neutral defects even in the case of device layers with thicknesses of tens of nm.
Publications
- Hydrogen donor in anatase TiO2, Phys. Rev. B 93, p. 045204, 2016
E. V. Lavrov
(See online at https://doi.org/10.1103/PhysRevB.93.045204) - Photoconductive detection of hydrogen in ZnO and rutile TiO2, J. Appl. Phys. 120, p. 055703, 2016
E. V. Lavrov, T. Mchedlidze, and F. Herklotz
(See online at https://doi.org/10.1063/1.4960132) - Hydrogen donors in ZnO and TiO2, Proc. SPIE 10036, p. 1003618, 2017
E. V. Lavrov
(See online at https://doi.org/10.1117/12.2245420) - Hydrogen motion in rutile TiO2, Sci. Rep. 7, p. 17065, 2017
A. J. Hupfer, E. V. Monakhov, B. G. Svensson, I. Chaplygin, and E. V. Lavrov
(See online at https://doi.org/10.1038/s41598-017-16660-3) - Photoconductity as a method to probe defects in ultra thin Si films, Appl. Phys. Lett. 110, p. 132102, 2017
E. V. Lavrov, I. Chaplygin, and T. Mchedlidze
(See online at https://doi.org/10.1063/1.4979276) - On the method of photoconductive detection of defects in semiconductors by vibrational mode-related Fano resonances, J. Appl. Phys. 124, p. 025704, 2018
F. Herklotz, I. Chaplygin, and E. V. Lavrov
(See online at https://doi.org/10.1063/1.5037412)
