Viena iš pagrindinių priežasčių, keičiančių puslaidininkinių prietaisų parametrus, yra elektriškai aktyvūs defektai. Gilieji lygmenys sąlygoja krūvininkų gyvavimo trukmės mažėjimą medžiagoje, todėl blogėja krūvininkų surinkimo koeficientas puslaidininkiniuose detektoriuose, išauga energijos nuostoliai galios prietaisuose bei mažėja šviesos diodų našumas. Elektriškai aktyvių radiacinių bei technologinių defektų charakterizavimas yra aktualus vystant naujų, daugiasluoksnių puslaidininkinių struktūrų formavimo technologijas bei puslaidininkinių detektorių darbo parametrų optimizavimui. Šiame darbe buvo sukurta nesąlytinė laike išskirtosios spektroskopijos metodika giliųjų lygmenų puslaidininkinėse struktūrose įvertinimui kambario temperatūroje. Ši metodika įgalina sinchroniškai kontroliuoti gaudyklių aktyvacijos energiją ir krūvininkų gyvavimo trukmę. Sukurtas, išbandytas ir sukalibruotas mikrobangomis zonduojamo fotolaidumo kinetikų matavimo prietaisas, skirtas krūvininkų gyvavimo trukmės bandinio briaunoje ir plokštumoje įvertinimui bei technologinių procesų kontrolei. Šiais metodais buvo įvertinti defektų parametrai hadronais apšvitintame, įvairiais metodais užaugintame Si. Taip pat įvertinta legiravimo, metalų implantacijos ir apšvitinimų įtaka Ge struktūrų rekombinacijos charakteristikoms. Rekombinacijos parametrų kontrolei apšvitų stabdomais bei skvarbiaisiais hadronais metu buvo sukurta nuotoliniu būdu valdoma matavimų sąranga ir pritaikyta radiacinių defektų tipų ir jų... [toliau žr. visą tekstą] / Electrically active defects are one of the main obstacles to produce high efficiency semiconductor based devices. Deep levels determine the non-radiative recombination processes and deteriorate efficiency of light emitting diodes, charge collection efficiency of radiation detectors and determine high power dissipation of the power devices. This work is addressed to material science and development of contactless measurement technologies for non-invasive defects characterization and identification within modern structures of Si, Ge and GaN by developing the non-destructive techniques. Contactless time resolved techniques for deep levels spectroscopy has been approved for evaluation of defects parameters within irradiated Si and implanted Ge structures. Peculiarities of recombination parameters have been revealed in Ge structures dependent on doping and irradiation. The methodology and instrumentation for the control of recombination parameters during irradiations by penetrative and stopped protons have been proposed, designed and approved. Evolution of densities and of species of the radiation defects during irradiation has been examined and models for fluence dependent variations of density of extended defects are proposed. An impact of dislocation networks on recombination properties has been revealed within strained thin-layered SiGe structures and epitaxial GaN layers. The models for explanation of the interplay of defects in these structures have been proposed in this... [to full text]

Title: Photoconductivity, photoluminescence and charge collection in semiinsulating CdTe and CdZnTe Author: Jakub Zázvorka Department: Institute of Physics of Charles University Supervisor of the doctoral thesis: prof. Ing. Jan Franc, DrSc., Institute of Physics of Charles University. Abstract: Cadmium telluride and its compounds with zinc are the material of choice in spectroscopic room temperature high energy radiation detectors. The development of the final device is influenced by many parameters, including material impurities and defects, homogeneity and surface preparation. This thesis offers a comprehensive investigation of the detector fabrication process and of the parameters and physical effects influencing the spectroscopic resolution and performance of the detector. Structure of deep levels is investigated through photoluminescence and correlated with other electro-optical measurements dealing with the impact of structural imperfections of the material and their effect. The influence of resistivity and photoconductivity homogeneity on the detector performance is studied through electrical measurement of the charge carrier transport and charge collection of the sample. Obtained results are explained using the Fermi level shift theory and confronted with a theoretical model and calculations. The...

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Creation of semi-insulating layers in SiC is highly desirable for high voltage device fabrication. Specifically PiN diodes can be fabricated with a compensated semi-insulating layer that would be capable of blocking a large reverse voltage. Semi-insulating (SI) behavior in SiC has been traditionally achieved via passivation of shallow dopants with vanadium-related deep levels. Degraded electrical properties of SiC devices result from the use of vanadium compensated SiC because unintentional formation of additional defects due to vanadium segregation and stress generation in the material occur. In this work, the possibility of low doped or SI epilayers via engineering of the boron related defects in SiC is investigated. High temperature treatment (up to 2000°C) of boron doped samples is used to stimulate boron diffusion and formation of deep boron centers in concentration sufficient for compensation of shallow dopants, without simultaneous formation of undesirable shallow boron levels. High temperature annealing of both epitaxial layers in-situ doped with boron and boron implanted 4H-SiC is investigated. The possibility of diffusion from highly boron doped substrate is also investigated. The diffusion profiles are modeled and the diffusion coefficients extracted to give information about diffusion mechanisms. The boron D-center was observed using photoluminescence (PL) after high temperature annealing of the implanted samples. Clear temperature dependence of the creation of the D-center was observed. Compensated material was revealed after an Inductively Coupled Plasma (ICP) etch on an epi-over grown sample.

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Title: Photo-Hall effect spectroscopy and laser-induced transient currents in CdTe-based semiconductor radiation detectors Author: Artem Musiienko Department / Institute: Institute of Physics, Faculty of Mathematics and Physics, Charles University Supervisor of the doctoral thesis: Prof. RNDr. Roman Grill, CSc, Institute of Physics, Faculty of Mathematics and Physics, Charles University Abstract: Cadmium Telluride, Cadmium Zinc Telluride, and Cadmium Manganese Telluride are important semiconductors with applications in radiation detection, solar cells, and electro-optic modulators. Their electrical and optical properties are principally controlled by defects forming energy levels within the bandgap. Such defects create recombination and trapping centers capturing photo- created carriers and depreciating the performance of the detector. Simultaneously, the changed occupancy of levels leads to the charging of detector's bulk, which results in the screening of applied bias and the loss of detector's sensitivity. Detailed knowledge of crystal defect structure is thus necessary for the predictable detector work and also for the possibility to reduce the structural defects concentration. This thesis reports on the investigation of deep energy levels in CdTe-based high resistivity and detector-grade materials by...

Title: Point defects in materials for detection of X-ray and gamma radiation Author: Martin Rejhon Department: Institute of Physics of Charles University Supervisor: prof. Ing. Jan Franc, DrSc., Institute of Physics of Charles Uni- versity Abstract: Cadmium telluride and its compounds are suitable materials for pro- duction of X-ray and gamma-ray detectors working at room temperature. How- ever, the detector quality is affected by material imperfections, such as crystal defects and impurities. It results into forming of deep levels which act as re- combination and trapping centers. Then, the accumulated space charge at these deep levels influences electric and spectroscopic properties of the detector. In the end it may result in the polarization effect, when the electric field is localized in vicinity of one contact and detection properties are decreased. This thesis reports a complex study of a detector band structure by various meth- ods with focus on differences between CdTe, CdZnTe, CdTeSe and CdZnTeSe. The electro-optic Pockels effect is used to investigate the influence of the illumi- nation in range 900 − 1800 nm on the inner electric field. The temperature and time evolutions of the electric field after application of bias or switching of the additional light at 940 nm were measured to determine deep levels...

Title: Point defects in materials for detection of X-ray and gamma radiation Author: Martin Rejhon Department: Institute of Physics of Charles University Supervisor: prof. Ing. Jan Franc, DrSc., Institute of Physics of Charles Uni- versity Abstract: Cadmium telluride and its compounds are suitable materials for pro- duction of X-ray and gamma-ray detectors working at room temperature. How- ever, the detector quality is affected by material imperfections, such as crystal defects and impurities. It results into forming of deep levels which act as re- combination and trapping centers. Then, the accumulated space charge at these deep levels influences electric and spectroscopic properties of the detector. In the end it may result in the polarization effect, when the electric field is localized in vicinity of one contact and detection properties are decreased. This thesis reports a complex study of a detector band structure by various meth- ods with focus on differences between CdTe, CdZnTe, CdTeSe and CdZnTeSe. The electro-optic Pockels effect is used to investigate the influence of the illumi- nation in range 900 − 1800 nm on the inner electric field. The temperature and time evolutions of the electric field after application of bias or switching of the additional light at 940 nm were measured to determine deep levels...

Neste trabalho estudamos a estrutura eletrônica de defeitos pontuais em diamante , os quais introduzem níveis profundos na faixa proibida deste material. Utilizamos o modelo de aglomerado molecular dentro de dois formalismos: o Método do Espalhamento Múltiplo X (MS- X), que é um método de primeiros princípios e o método \"Complete Neglect of Differential Overlap\" (CNDO/ BW), que é semi-empírico. Foi empregado um tratamento adequado para os orbitais de superfície em cada um dos dois formalismos . Foram estudados dois sistemas: o Nitrogênio substitucional e a vacância simples. Para o Nitrogênio, analisamos as possíveis distorções associadas a este centro, procurando interpretar os resultados experimentais. A vacância simples mostrou-se ser um sistema bastante semelhante à vacância simples em Silício: em ambos os casos observa - se uma distorção Jahn-Teller. O modelo adotado mostrou- se capaz de descrever satisfatoriamente as estruturas eletrônicas dos dois centros estudados, fornecendo resultados quantitativos que são comparados com a experiência . / In this work we studied the electronic structure of point defects in diamond. To do this we used the molecular cluster model within two formalisms: the first-principles X Scattered wave method MS-X ) and the semiempirical Complete Neglect of Differential Overlap (CNOO/BW) method. In each case, an adequate surface orbitals treatment was utilized. We studied the following systems: the substitutional Nitrogen and the simple neutral vacancy. For the substitutional Nitrogen. We analyzed the possible distortion related to this center trying to interprete the experimental results. For the simple neutral vacancy in diamond. The results showed to be similar to the simple Silicon vacancy picture: In both cases we observed a Jahn-Teller distortion (lowering the symmetry of the center). The adopted model showed to be able to describe satisfactorily their electronic structures, and quantitative results are given, which are compared with the experimental data.