Papers by Author: Edvins Dauksta

Abstract: The enhancement of CdZnTe crystal resistivity by λ=1064nm Nd:YAG laser radiation was shown. This effect is explained by compensation of cadmium vacancy (V_Cd) by indium atoms due to a laser-induced temperature gradient around Te inclusions. The temperature gradient is caused by the selective absorption of the laser radiation by the Te inclusions.

Abstract: Semiconductor Hg₃In₂Te₆ crystals and their analogous are solid solutions of In₂Te₃ and HgTe. Hg₃In₂Te₆ crystals are congruently melted as chemical compound. Like In₂Te₃ the Hg₃In₂Te₆ crystal has cubic crystal lattice with stoichiometric vacancies in their crystal structure. The electroconductivity, photoconductivity, mechanical, chemical properties of the crystals do not deteriorate after their irradiation by γ-photons with energies up to 1 MeV and doses up to 10¹⁸ cm^-2 , by electrons with energies up to 300 MeV and doses up to 10¹⁹ cm^-2 and by mixed reactor irradiation (filtered slow neutrons) with doses up to 10¹⁹ cm^-2 [1,2]. This feature is determined by high concentration (~10²¹ cm^-3) of stoihiometric vacancies (V_s) in crystal structure, where every third In-cation node is empty. These V_s are electroneutral, they capture all impurity atoms in these crystals and kept them in electroneutral state too. On the other hand this feature doesn't allow to form direct p-n junctions in these crystals by introducing the impurities. However, we have developed p-n junction analogues in form of Schottki diodes and corresponding photodiodes with semitransparent metal layer on single crystal Hg₃In₂Te₆ substrate that allows irradiation to get into active region preserving this way all the advantages compared to p-n junction.

Abstract: A possibility of formingquantum cones (QC) by Nd:YAG laser radiation on the surface of semiconductorssuch as Si and Ge crystals, and SiGe and CdZnTe solid solutions has been shown.A two-stage mechanism of quantum cone formation has been proposed. The first stage is generation and redistribution of point defects (impurity atoms and intrinsic point defects – vacancies and self-interstitials) in a temperature gradient field, the so-called thermogradient effect. As a result a new phase is formed on the irradiated surface, for example a Ge phase forms on the surface of a SiGe solid solution. The second stage is characterized by mechanical plastic deformation of the strained top layer leading to the formation of quantum cones, due to selective laser radiation absorption of the top layer. The first stage is more difficult for understanding of the physical processes which takeplace during of growth of QC, especially in pure intrinsic elementary semiconductors (Ge, Si) and compounds (CdTe, GaAs). Therefore, this research is focused on the investigation of the first stage of QC formation by laser irradiation. As a result of the investigation, a new mechanism for p-n junction formation in the elementary semiconductors and heterojunction in solid solutions by laser radiation as a first stage of QC formation is proposed.

Abstract: The research report is devoted to the development of a new method of nanostructures formation in ITO/p-Si/Al structure with powerful laser radiation and study of its optical and electrical properties for solar cells applications. It was shown that after the structure irradiation by Nd:YAG laser second harmonic, dark current voltage characteristics become diode-like. Increase of ITO/p-Si/Al solar cell efficiency after irradiation by the laser, using photocurrent voltage characteristic method, was shown.

Abstract: Photoluminescence mechanisms (models) are reviewed and experimental data are analyzed based on our model, related to direct radiative transitions from the second conduction sub-band to the first one.

Abstract: It was shown the possibility to improve ZnO crystal lattice by powerful Nd:YAG laser radiation. The measurements of photoluminescence spectra have shown the decrease of the spectra intensity of defect related band with maximum at 2.4 eV after irradiation by laser. The control of photoluminescence spectra intensity of defect related band was achieved by different laser radiation intensity. Topography studies using atomic force microscope showed smoothing of the surface, as well. The formation of nanocavities on ZnO/Si sample surface at higher laser radiation intensity was detected by scanning electron microscope.

Abstract: The possibility to form “black silicon” on the surface of Si structure by Nd:YAG laser radiation has been shown. The shape and height of micro-cone structure strongly depends on Nd:YAG laser intensity and number of laser pulses. Light is repeatedly reflected between the cones in the way that most of it is absorbed. Si micro-cone structure spectral thermal radiation is close to black body spectral radiance, which makes this structure useful for solar cells application. The micro-chemical analysis performed by SEM has shown that the microstructures contain NiSi2. This was approved by presence of LO phonon line in Raman back scattering spectrum. The control of micro-cone shape and height was achieved by changing the laser intensity and number of pulses.

Abstract: The influence of strongly absorbing N¬2 laser radiation on pores formation on a surface of Si single crystal has been investigated using optical microscope, atomic force microscope and photoluminescence. After irradiation by the laser and subsequent electrochemical etching in HF acid solution morphological changes of the irradiated parts of a surface of Si were not observed. At the same time, pores formation on the non-irradiated parts of Si surface took place. The porous part of the Si surface is characterized by strong photoluminescence in red part of spectra with maximum at 1.88 eV and intensity of photoluminescence increases with current density. Suppression of the pores formation by the laser radiation is explained with inversion of Si type conductivity from p-type to n-type. This fact is explained by Thermogradient effect – generation and redistribution of the intrinsic defects in gradient of temperature. It was shown that the depth of n-Si layer on p-Si substrate depends on intensity of laser radiation and it increases with intensity of laser radiation. The results of the investigation can be used for optical recording and storage of information on surface of semiconductors.