@phdthesis{Holla2016, author = {Holla, Markus}, title = {Defektcharakterisierung von Halbleitermaterialien f{\"u}r die Photovoltaik}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-36384}, school = {BTU Cottbus - Senftenberg}, year = {2016}, abstract = {Zur Deckung des stetig steigenden Energiebedarfs und unter Ber{\"u}cksichtigung des Umweltschutzes werden unter anderem Solarzellen genutzt. Defekte in Solarzellen k{\"o}nnen die Effizienz verringern. In dieser Arbeit wird das Defektverst{\"a}ndnis von Silizium basierten Solarzellen erweitert. Neue experimentelle Erkenntnisse konnten zu folgenden Schwerpunkten gewonnen werden: • Siliziumnitrid- und Siliziumkarbidausscheidungen in multikristallinem Silizium • Rekombinationsaktivit{\"a}t in d{\"u}nnen Siliziumschichten • Charakterisierung der Rekombinationsaktivit{\"a}t von Germanium als Modellmaterial f{\"u}r die Siliziumkristallisation • Rekombinationsaktivit{\"a}t und Verspannung an Korngrenzen Um Ergebnisse experimenteller Defektcharakterisierung auf allgemein g{\"u}ltige Parameter der Rekombination wie z.B. Ladungstr{\"a}gerdiffusionsl{\"a}nge oder Oberfl{\"a}chenrekombinationsgeschwindigkeit zur{\"u}ckf{\"u}hren zu k{\"o}nnen, wurden zu folgenden Ph{\"a}nomenen Modelle entwickelt und Simulationen durchgef{\"u}hrt: • Getterzonen an Korngrenzen • Ermittlung von Diffusionsl{\"a}nge und Diffusionskoeffizient in D{\"u}nnschichtmaterial • 3D-Raumladungseffekte Die Nutzung der gewonnenen Erkenntnisse {\"u}ber die Rekombinationseigenschaften der Defekte liegt in einer m{\"o}glicherweise zuk{\"u}nftigen kontrollierten Defektbeeinflussung und somit einer Effizienzverbesserung von Solarzellen.}, subject = {Defekt; Defect; Halbleiter; Semiconductor; Festk{\"o}rperphysik; Halbleiter}, language = {de} } @phdthesis{Jia2009, author = {Jia, Guobin}, title = {Characterization of electrical and optical properties of silicon based materials}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-14030}, school = {BTU Cottbus - Senftenberg}, year = {2009}, abstract = {In this work, the electrical and luminescence properties of a series of Si based materials used for photovoltaics, microelectronics and nanoelectronics have been investigated by means of electron beam induced current (EBIC), cathodoluminescence (CL), photoluminescence (PL) and electroluminescence (EL). Photovoltaic Si produced by block casting has been investigated by EBIC on wafers sliced from different parts of the ingot. The impact of selected solar cell processing steps on the material properties has been evaluated by EBIC utilizing adjacent wafers from the ingot. The temperature dependence of dislocations' EBIC contrast was measured to assess the degree of dislocation contamination with impurities, yielding low dislocation contamination for the middle of the block and high contamination in the top and bottom regions. This is in agreement with the impurity distribution in the block. It was found that phosphorus diffusion gettering (PDG) followed by SiN firing greatly reduces the recombination activity of extended defects at room temperature, and improves the bulk property simultaneously. The improvement is attributed to both PDG of metal impurities and a passivation effect of SiN firing. In order to better understand the factors limiting the properties of thin polycrystalline Si layers prepared by the Aluminum induced layer exchange (Alile) technique, epilayers grown on (111) and (100) monocrystalline Si substrates were used as a model system to investigate the impact of processing temperature (Ts) and type of substrate. It was found that no dislocations are formed for epilayers on (100) Si, while a high density of dislocations was detected on epilayers prepared on (111) Si at 450 °C. The dislocation density decreases with increasing TS. The diffusion lengths extracted from the energy dependent EBIC collection efficiencies reveal an improvement of the epilayer quality with increasing TS during growth from 450 °C to 650 °C, and a decrease of the epilayer quality at 700 °C. This is attributed to a reduction of the dislocation density with increasing TS and a formation of precipitates during the process. Precipitate formation of at 700 °C is limited because the metal impurities are very mobile at high TS, resulting in a homogeneous distribution of the impurities. Because the impurities are effective lifetime killers of the minority carriers, so the diffusion length decreases. PL measurements on epilayers grown on Si substrates revealed no characteristic dislocation-related luminescence (DRL) lines at room temperature and 77 K, while intense characteristic DRL lines D1 - D4 have been detected in the sample prepared by the Alile technique. This indicates that dislocations in the Alile sample are relatively clean. The possible reason for the purification of the Alile samples is Al induced gettering during the polycrystalline Si layer growth. The diffusion length in the thin top layer of Si-on-insulator (SOI) samples has been successfully measured by EBIC employing suppression of the surface recombination at the buried oxide layer and at surface of the top layer by biasing. The measured diffusion length is several times larger than the layer thickness. Dislocation networks produced by Si wafer direct bonding have been investigated with regard to their electrical properties by EBIC. The networks were observed to show charge carrier collection and electrical conduction. Inhomogeneities in the charge collection were detected in n- and p-type samples under appropriate beam energy. The EBIC contrast behavior can be understood under the consideration of the positively charged oxide precipitates along with dislocations charged with majority carriers, where the appearance of the contrast in dark or bright depends strongly on the ratio of the collection and the recombination loss of the carriers.The luminescence properties of Si nanostructures (Si nanowires, Si nano rods, porous Si, and Si/SiO2 multi quantum wells (MQWs)) are another important subject of this work. Sub-bandgap infrared (IR) luminescence around 1570 nm has been found in Si nanowires, nano rods and porous Si. PL measurements with samples immersed in different liquid media, for example, in aqueous HF (50\%), concentrated H2SO4 (98\%) and H2O2 established that the sub-bandgap IR luminescence originates from the Si/SiOx interface. Its origin was explained in terms of a simple recombination model through radiative interface states. EL in the sub-bandgap IR range has been observed in simple diodes prepared on porous Si and MQWs at room temperature. The results show the possibility to fabricate an efficient light emitter around 1570 nm wavelength based on the radiative recombination at the Si/Si oxide interface. Based on the knowledge about radiative transitions via the interface states, an improved understanding of luminescence in dislocated samples was proposed.}, subject = {Siliciumverbindungen; Werkstoffkunde; Silicium; Elektrische Eigenschaft; Optische Eigenschaft; Versetzungsnetzwerk; Elektrische Leitf{\"a}higkeit; Diffusionsl{\"a}nge in SOI-Schichten; Solarzellen; Infrarote Lumineszenz im Sub-bandgap-Bereich; Dislocation network; Electrical conductivity; Diffusion length in SOI layer; Solar cells; Sub-bandgap infrared luminescence from Si/SiOx interface}, language = {en} } @phdthesis{Trushin2011, author = {Trushin, Maxim}, title = {Electronic properties of interfaces produced by silicon wafer hydrophilic bonding}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-22841}, school = {BTU Cottbus - Senftenberg}, year = {2011}, abstract = {The thesis presents the results of the investigations of electronic properties and defect states of dislocation networks (DNs) in silicon produced by wafers direct bonding technique. Practical interest for the investigations in this area issued - first of all - from the potential application of such dislocation networks in microelectronics as all-Si light emitter for on-chip interconnection. Besides, dislocation networks may serve as a perfect model object to get new information about the fundamental properties of dislocations and grain boundaries in Si, what is of particular importance for multicrystalline silicon solar cells performance. Despite of a long story of studying of dislocations in silicon, a new insight into the understanding of their very attractive properties was succeeded due to the usage of a new, recently developed silicon wafer direct bonding technique, allowing to create regular dislocation networks with predefined dislocation types and densities. Samples for the investigations were prepared by hydrophilic bonding of p-type Si (100) wafers with same small misorientation tilt angle (~0,5°), but with four different twist misorientation angles Atw (being of <1°, 3°, 6° and 30°, respectively), thus giving rise to the different DN microstructure on every particular sample. The main experimental approach of this work was the measurements of current and capacitance of Schottky diodes prepared on the samples which contained the dislocation network at a depth that allowed one to realize all capabilities of different methods of space charge region spectroscopy (such as CV/IV, DLTS, ITS, etc.). The key tasks for the investigations were specified as the exploration of the DN-related gap states, their variations with gradually increasing twist angle Atw, investigation of the electrical field impact on the carrier emission from the dislocation-related states, as well as the establishing of the correlation between the electrical (DLTS), optical (photoluminescence PL) and structural (TEM) properties of DNs. The most important conclusions drawn from the experimental investigations and theoretical calculations can be formulated as follows: - DLTS measurements have revealed a great difference in the electronic structure of small-angle (SA) and large-angle (LA) bonded interfaces: dominating shallow level and a set of 6-7 deep levels were found in SA-samples with Atw of 1° and 3°, whereas the prevalent deep levels - in LA-samples with Atw of 6° and 30°. The critical twist misorientation angle separating SA- and LA- interfaces was estimated as Atw*≈ 3,5±0,5°, what agrees quiet well with the results of previous PL and TEM investigations. - For the dominating shallow traps in SA-samples (denoted as ST1/ST3 traps) a new phenomenon - that is 'giant Poole-Frenkel effect' of enhanced carrier emission due to dislocations elastic strain field was observed for the first time. Performed theoretical calculations have shown that in the investigated samples such an effect should be ascribed to the row of 60° dislocations rather than to the mesh of screw ones. In this respect, shallow traps ST1/ST3 were identified either with shallow 1D bands (directly or as being coupled with them) or with shallow stacking fault states on splitted 60° dislocation. - From the comparison and correlations of measured DLTS spectra with the results of PL and TEM investigations it was established, that shallow ST1/ST3 traps participate in D1 radiative recombination and that the structural elements, responsible for D1 luminescence of small-angle DNs, are the triple knots (intersections with screw dislocations) along the 60° dislocations. However, the optimal density of 60° dislocations as well as of triple knots, in other words - the optimal tilt and twist misorientation angles for maximal D1 intensity - needs further clarification.}, subject = {Elektronische Eigenschaft; Siliciumbauelement; Bonden; Wafer; Silicium; Versetzungsnetzwerk; Poole-Frenkel Effekt; DLTS; D1 Lumineszenz Band; Dislocation networks; DLTS; Poole-Frenkel effect; D1 Luminescence band}, language = {en} } @phdthesis{Oriwol2014, author = {Oriwol, Daniel}, title = {Die Versetzungsstruktur von multikristallinem Silicium aus der industriellen VGF-Blockkristallisation}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-31553}, school = {BTU Cottbus - Senftenberg}, year = {2014}, abstract = {Die vorliegende Arbeit befasst sich mit der Struktur und der Entwicklung von Versetzungen in multikristallinen Siliciumbl{\"o}cken aus der gerichteten Blockkristallisation. Versetzungen k{\"o}nnen f{\"u}r die Rekombination von Ladungstr{\"a}gern verantwortlich sein und damit den Wirkungsgrad von Solarzellen und -modulen mindern. Die experimentelle Arbeit gliedert sich bez{\"u}glich ihrer Fragenstellung und der Methodenwahl in drei Teile und wird in den Kapiteln 2 bis 4 behandelt. In Kapitel 2 wird die Defektstruktur vieler Siliciumbl{\"o}cke mittels automatisierten Verfahren untersucht. Die Analysemethoden umfassen dabei die Auswertung der Wafertextur und der Infrarot-Durchlichtbilder sowie {\"A}tzgrubendichtez{\"a}hlung (EPD) und Photolumineszenz (PL). Der Betrachtungsabstand ist makroskopisch und die Ergebnisse geben das Verhalten von vielen Versetzungen wieder. Die Versetzungsstruktur in multikristallinem Silicium ist gepr{\"a}gt durch scharf abgegrenzte Bereiche mit sehr hoher Versetzungsdichte. Diese sog. Versetzungscluster bestehen aus einem Netzwerk aus Versetzungs-Pile-ups (Kleinwinkelkorngrenzen) und k{\"o}nnen in sogenannte leichte und dichte Cluster unterschieden werden. Die Versetzungscluster haben im Siliciumblock einen Ausgangspunkt, von dem aus sie sich ausbreiten. Dieser befindet sich haupts{\"a}chlich an Korngrenzen und generiert sich spontan w{\"a}hrend der Erstarrung in der N{\"a}he der Phasengrenze. Das Auftreten von leichten und dichten Clustern ist abh{\"a}ngig von der Kornorientierung parallel zur Wachstumsrichtung. K{\"o}rner mit Orientierungen nahe <111>, <211> und <311> neigen dazu leichte Cluster auszubilden, w{\"a}hrend K{\"o}rner mit Orientierungen um <110>, <331> und <531> eher dichte Cluster ausbilden. Kornorientierungen um <100> und <511> sind unauff{\"a}llig bzgl. der Ausbildung von Versetzungsclustern. Der Zusammenhang liegt in der Orientierung der Gleitebenen begr{\"u}ndet. Kapitel 3 behandelt die strukturelle Untersuchung der Versetzungen mit der Transmissionselektronenmikroskopie (TEM) sowie der Synchrotron- R{\"o}ntgentopographie (WB-XRT). Die Versetzungen formen streng geordnete Pile-ups, welche letztendlich Kleinwinkelkorngrenzen entlang der Wachstumsrichtung ausbilden. Der Versetzungsabstand betr{\"a}gt etwa 30 bis 800 nm, was mit einer Verkippung in der Kristallorientierung von 0,3 bis 0,07 ° korrespondiert. Die Rotation der Kristallorientierung verl{\"a}uft haupts{\"a}chlich um eine Achse parallel zur Wachstumsrichtung. Anhand dieser Beobachtungen wurde ein Modell zur Absch{\"a}tzung der Versetzungsdichte aufgestellt. F{\"u}r die leichten Cluster betr{\"a}gt diese ca. 2*10^5 cm^2 und f{\"u}r die dichten Cluster etwa 3*10^7 cm^2. Die Auswirkungen der Versetzungsstruktur auf die elektrischen Eigenschaften werden in Kapitel 4 behandelt. Mit Electron Beam Induced Current (EBIC) und Dunkel-Lock-In-Thermographie (DLIT) wurde herausgestellt, dass vor allem solche Versetzungen elektrisch aktiv sind, welche sich zu Kleinwinkelkorngrenzen angeordnet haben. Ein niedriger Versetzungsabstand innerhalb der Subkorngrenzen scheint nur eine Bedingung f{\"u}r eine elektrische Aktivierung zu sein. Ein Zusammenhang zwischen dem Betrag der Verkippung einer Subkorngrenze und dem EBIC-Kontrast konnte nicht hergestellt werden. In der abschließenden Diskussion (Kap. 5) wird ein Modell zur Entstehung und Evolution von Versetzungsclustern vorgeschlagen. Die Versetzungscluster generieren sich haupts{\"a}chlich an Korngrenzen. Dabei werden die Kleinwinkelkorngrenzen durch die Restrukturierung von Versetzungen sekund{\"a}r gebildet. Die Ergebnisse legen nahe, dass dies w{\"a}hrend der Erstarrung unmittelbar nach der Phasengrenze geschieht. Die treibenden Kr{\"a}fte sind demnach thermische Spannungen an der Erstarrungsfront. Die Versetzungen und damit die Subkorn-Strukturen erreichen die Phasengrenze und bleiben bei der weiteren Kristallisation erhalten, sodass die kontinuierlich auftretenden thermischen Spannungen mit neuen Versetzungen und damit mit erneuter Bildung von Versetzungen und Subkorngrenzen abgebaut werden m{\"u}ssen. Durch diesen Vererbungseffekt erh{\"o}ht sich die Versetzungsdichte stetig mit steigender Blockh{\"o}he. Im Abschluss werden Maßnahmen zur Reduktion der Versetzungsdichte im Kristallisationsprozess diskutiert. Beim Ankeimen am Tiegelboden oder w{\"a}hrend der Erstarrung sollten geeignete Kornorientierungen bevorzugt werden. Eine weitere Maßnahme ist die Reduktion der radialen thermischen Spannungen w{\"a}hrend der Kristallisation. Unbekannt bleibt die genaue, atomare Ursache der erh{\"o}hten Versetzungsgeneration an Korngrenzen und die damit verbundene spontane Bildung von Versetzungsclustern. Weiterhin bleibt offen, ob und in welchem Umfang Lomer-Cottrell-Versetzungen innerhalb der Subkorngrenzen gebildet werden und welchen Einfluss diese auf die elektrische Aktivit{\"a}t haben.}, subject = {Versetzungen; Multikristallines Silicium; Gerichtete Erstarrung; Synchrotron R{\"o}ntgentopographie; Transmissionselektronenmikroskopie; Dislocation; Multicrystalline silicon; Directional soldification; Synchrotron X-Ray topography; Transmission electron microscopy; Silicium; Polykristall; Versetzung }, language = {de} } @phdthesis{Wiatrek2013, author = {Wiatrek, Andrzej}, title = {Untersuchung der Eigenschaften der ges{\"a}ttigten stimulierten Brillouin-Streuung und ihrer Anwendungsm{\"o}glichkeiten}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-29577}, school = {BTU Cottbus - Senftenberg}, year = {2013}, abstract = {Es ist wohl gerade die Einfachheit seiner Erzeugung, welche den nichtlinearen optischen Effekt der stimulierten Brillouin-Streuung so interessant f{\"u}r viele Anwendungen in der optischen Signalverarbeitung, der Fasersensorik, der hochaufl{\"o}senden Spektroskopie und auch der Signalverz{\"o}gerung und -speicherung macht. Die geringe Verst{\"a}rkungsbandbreite kann zur selektiven Filterung oder Abtastung optischer Signale eingesetzt werden, was die Grundlage der optischen Spektroskopie aber auch der Lichtspeicherung ist. Dar{\"u}ber hinaus werden Signale innerhalb dieser Bandbreite nicht nur verst{\"a}rkt, sondern auch abh{\"a}ngig vom Gewinn bzw. der eingestellten Pumpleistung verz{\"o}gert. Diese Eigenschaft ist die Grundlage der sogenannten Slow-Light-Systeme. Damit kann mit einem Brillouin-Verst{\"a}rker ein durchstimmbarer optischer Kurzzeitpuffer realisiert werden. In der vorliegenden Arbeit werden mit Hilfe gezielt ges{\"a}ttigter Brillouin-Verst{\"a}rker grundlegende Beschr{\"a}nkungen des Brillouin-basierten Slow-Light und der Brillouin-basierten optischen Filterung aufgehoben, was mit den herk{\"o}mmlichen linearen Ans{\"a}tzen nicht m{\"o}glich ist. Der Vorteil der S{\"a}ttigung des Brillouin-Verst{\"a}rkers ist, dass sie nur zu einer vorhersagbaren Begrenzung des Amplitudenspektrums aber nicht zur Entstehung neuer Signalfrequenzen f{\"u}hrt. Die spektrale Begrenzung des verst{\"a}rkten Signals und ein nichtlinearer Verlauf der Gruppenlaufzeit im spektralen Randbereich des Brillouin-Verst{\"a}rkers f{\"u}hren zu einer zeitlichen Verbreiterung der verz{\"o}gerten Lichtpulse. Diese Verbreiterung ist insofern problematisch, dass sie die Unterscheidbarkeit der verschiedenen Signalpegel f{\"u}r logische Einsen und Nullen signifikant verschlechtert. Mit Hilfe des vorgestellten ges{\"a}ttigten Systems erfolgt eine gezielte R{\"u}ckformung der verz{\"o}gerten Pulse, was erstmalig zu einer verbreiterungsfreien und damit auch verlustarmen Pulsspeicherung f{\"u}hrt. Dar{\"u}ber hinaus kann auf Basis der Nachbildung der ges{\"a}ttigten Filtercharakteristik mit einem linearen Brillouin-Verst{\"a}rker ebenfalls eine verbreiterungsfreie Pulsverz{\"o}gerung nachgewiesen werden. Ein optischer Speicher kann aber auch durch Unterabtastung eines Signalspektrums mit einem Brillouin-basierten Kammfilter realisiert werden. Die maximale Speicherzeit ist dabei durch die nat{\"u}rliche Brillouin Gewinnbandbreite begrenzt. Dieser Wert ist abh{\"a}ngig von der Pump- und Signalleistung, der Umgebungstemperatur, von mechanischem Stress und vom Fasermaterial. Unter Ausnutzung der S{\"a}ttigungseigenschaften des Brillouin-Gewinns l{\"a}sst sich die Gewinnbandbreite durch {\"U}berlagerung einer s{\"a}ttigenden Spektralblende nahezu beliebig verkleinern. In dieser Arbeit wird auf Basis dieser Methode eine Bandbreitenreduktion des Brillouin-Filters um etwa eine Gr{\"o}ßenordnung nachgewiesen, wobei das Potential zur Verringerung um mehrere Gr{\"o}ßenordnungen besteht.}, subject = {Nichtlineare Optik; Brillouin-Streuung; Nichtlineare Optik; Stimulierte Brillouin-Streuung; Slow-Light; Nonlinear optics; Stimulated Brillouin scattering; Slow light}, language = {de} } @phdthesis{Schmidtbauer2013, author = {Schmidtbauer, Jan}, title = {MBE growth and characterization of germanium nanowires}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-28660}, school = {BTU Cottbus - Senftenberg}, year = {2013}, abstract = {Semiconductor nanowires, also called nanorods or nanowhiskers, are of particular interest for various applications in nanotechnology. Especially, germanium as a CMOS compatible material with its good electronic properties has gained renewed interest in recent years due to the availability of modern gate dielectrics. The present work deals with the vapor-liquid-solid growth of germanium nanowires and their characterization. The Growth has been carried out by means of molecular beam epitaxy using differently oriented germanium and silicon substrates whereas gold has been used to create metal catalyst droplets with radii of typically 100 nm and below. All stages from the substrate preparation to the final growth have been investigated in the frame of this work to find significant control parameters that influence the growth result. The droplet formation by means of gold evaporation onto the heated substrates has been investigated extensively on different substrates and for different surface preparations to identify parameters that are crucial for the resulting size distribution. Thereby sticking effects of the droplet circumference turned out to influence the radius distribution significantly. Germanium nanowires have been observed to grow preferentially along the <011> crystallographic directions on all utilized substrate orientations leading to defined possible inclinations of the wires with respect to the substrate normal. In contrast to the faceting known from silicon wires, the sidewalls mainly exhibit four flat {111} facets whereas the tip is roof shaped consisting of another two {111} facets. Different models which describe the inclined growth are presented and discussed. Furthermore, the material transport during the growth has been investigated. The nanowire length was found to be up to eight times larger than the nominal layer thickness according to the total amount of deposited germanium which is explained by surface diffusion towards the nanowires. The diffusion dominated growth regime was confirmed by length-radius-plot showing a decrease of the nanowire length at increasing radii. A temperature dependent diffusion model has been utilized to describe the observed nanowire length as a function of the substrate temperature. Beside conventional nanowires, so-called in-plane nanowires which grow along the substrate surface have been studied. Like their vertically growing counterparts, they also tend to grow along <011> in-plane directions which is particularly distinct on Ge(011) substrates. However, the fraction of nanowires which are aligned along <011> is influenced by substrate imperfections which was intentionally affected by means of wet-chemical substrate preparation. In addition to the nanowire growth, techniques for selective catalyst removal as well as for nanowire embedding in an insulating, transparent matrix have been established which can be important prerequisites for further nanowire processing in terms of electric or optoelectronic applications.}, subject = {Nanodraht; Germanium; Molekularstrahlepitaxie; Nanodr{\"a}hte; Molekularstrahlepitaxie; Germanium; Oberfl{\"a}chendiffusion; Nanostrukturen; Nanowire; Molecular beam epitaxy; Germanium; Surface diffusion; Nucleation; Nanostructures}, language = {en} } @phdthesis{Melnik2018, author = {Melnik, Nauka}, title = {Untersuchung des Strahlungsdrucks auf d{\"u}nne Folien unter Weltraumbedingungen}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-45847}, school = {BTU Cottbus - Senftenberg}, year = {2018}, abstract = {Trifft elektromagnetische Strahlung auf einen K{\"o}rper, geben die Photonen ihren Impuls ab, bei einer idealen Reflexion sogar den doppelten Impuls. Auf die Oberfl{\"a}che des bestrahlten K{\"o}rpers wird somit eine Kraft ausge{\"u}bt. Dieser Strahlungsdruck ist extrem gering, jedoch ergeben sich unter speziellen Bedingungen, wie bei einer Anwendung im luftleeren Raum des Weltalls, konkrete effektive Einsatzbereiche. Die Anwendung des Strahlungsdrucks als Antriebsmittel im Bereich der Raumfahrt ist der Ausgangspunkt folgender Dissertation. Großfl{\"a}chige reflektierende Folien k{\"o}nnen den Strahlungsdruck der Sonne als spezielles Antriebsmittel f{\"u}r Raumfahrzeuge, sogenannte Sonnensegler, nutzen. Ziel dieser Arbeit ist die Entwicklung einer Messeinrichtung zur Analyse der Kraftwirkung durch sonnen{\"a}hnliche Strahlung auf d{\"u}nne, reflektierende Folien. Des Weiteren wird die Messeinrichtung durch verschiedene Messreihen verifiziert, auftretende Effekte werden charakterisiert. Die Messeinrichtung ist in einer Hochvakuumkammer installiert. Der Strahlungsdruck wird durch eine 1600W Xenon Lampe mit sonnen{\"a}hnlichem Spektrum auf eine 7,5 µm dicke, mit Aluminium beschichtete Kaptonfolie ausge{\"u}bt. Die resultierende Krafteinwirkung auf die Folienoberfl{\"a}che wird mittels einer Pr{\"a}zisionswaage gemessen. In mehreren Testreihen werden Folienproben unterschiedlichen Bestrahlungsst{\"a}rken ausgesetzt. Die experimentell ermittelten Messdaten best{\"a}tigen die theoretisch berechneten Werte des Strahlungsdrucks. Dar{\"u}ber hinaus zeigt sich im Verlauf der Experimente ein bisher unbeachteter Effekt. An der Folienoberfl{\"a}che haften unter Atmosph{\"a}re Wassermolek{\"u}lschichten, welche im Vakuum zun{\"a}chst an der Folie haften bleiben. Diese Molek{\"u}le werden erst bei Bestrahlung von der Oberfl{\"a}che desorbiert. Der Impuls durch die entweichenden Molek{\"u}le ist um ein Vielfaches gr{\"o}ßer als der Impuls der Photonen. Dieser Effekt beeintr{\"a}chtigt die Strahlungsdruckmessung. Um die st{\"o}renden Einfl{\"u}sse zu eliminieren, sind in einer Testprozedur Randbedingungen definiert worden.}, subject = {Strahlungsdruck; Sonnensegel; Pr{\"a}zisionswaage; Desorption; Radiation pressure; Solar sailing; High precision balance; Desorption; Strahlungsdruck; Sonnensegel ; Extraterrestrische Physik}, language = {de} } @phdthesis{Varlamova2013, author = {Varlamova, Olga}, title = {Self-organized surface patterns originating from femtosecond laser-induced instability}, isbn = {978-3-95404-604-1}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-29530}, school = {BTU Cottbus - Senftenberg}, year = {2013}, abstract = {The phenomenon of laser-induced periodic surface structures (LIPSS), or ripples, generated by near-infrared radiation with the central wavelength around 800 nanometer (λlaser ≈ 800 nm) and pulse duration about of 100 femtosecond (τpulse ≈ 100 fs) on solid targets is considered in this dissertation. The main aim of the work is a better understanding of the fundamental processes of laser-matter interaction resulting in pattern formation by femtosecond (fs) laser ablation. The problem is of great interest both in fundamental and applied science. The knowledge of the underlying physical mechanisms will provide the opportunity to control surface nanostructuring, which has a big application potential in many modern technologies. Femtosecond LIPSS observed at the bottom of ablation crater reveal a large variety of features including nanostructures with periods below 100 nm. Moreover, the ripple size depends mainly on the irradiation dose/absorbed laser energy and is rather insensitive to the variation of laser wavelength or incidence angle. The orientation of the structures is dictated by laser polarization. All these experimental observations and an astounding similarity of the structures to other patterns originating from instabilities led to the idea to attribute the femtosecond laser nanostructuring to a self-organized pattern formation from laser-induced surface instability. In this dissertation, surface pattern formation upon femtosecond laser ablation is considered in the framework of an adopted surface erosion model, based on the description of spontaneous pattern formation on surfaces bombarded with high-energy ions. We exploit the similarity to ion-beam sputtering and extend a corresponding model for laser ablation by including laser polarization. It has been found that an asymmetry in the deposition and dissipation of the incident laser energy, related to the laser polarization, results in a corresponding dependence of coefficients in a nonlinear equation of the Kuramoto-Sivashinsky type. The surface morphologies calculated in the framework of this model for different configurations of the incident laser electric field show an excellent qualitative agreement with structures observed in ultra-short pulse ablation experiments. In this work, properties of the periodic surface structures induced upon femtosecond laser ablation are studied in detail, focusing on a systematic investigation of the main control parameters regulating the pattern formation process. The results support the non-linear self-organization mechanism of pattern formation from laser-induced surface instability.}, subject = {Oberfl{\"a}chenstruktur; Mikromechanik; Laserablation; Ultrakurzzeitlaser; Femtosekundenlaserablation; Laser-induzierte Oberfl{\"a}chenstrukturierung; Ripples; Selbstorganisierte Strukturbildung; Femtosecond laser ablation; Laser-induced surface patterning; Ripples; Selforganized pattern formation}, language = {en} } @phdthesis{Mankovics2015, author = {Mankovics, Daniel}, title = {Luminescence investigation of bulk solar silicon and silicon thin films on glass substrate}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-35196}, school = {BTU Cottbus - Senftenberg}, year = {2015}, abstract = {The aim of this work is to study the optical properties of crystal defects in multicrystalline solar silicon and poly-/microcrystalline silicon thin films on glass substrate. First a setup for photoluminescence imaging on multicrystalline silicon solar wafers was developed. This system is suitable for detecting band-to-band luminescence as well as defect-related luminescence at room temperature on large-scale wafers at different stages of their processing. Spectroscopic photoluminescence investigations of multicrystalline silicon solar wafers indicated a new intense luminescence line at ≈ 0.91 eV at room temperature. The origin of this line is probably found in a specific grain boundary. Furthermore, luminescence in the region of 0.8 eV was investigated in detail, and it was found that probably oxygen is responsible for a peak at 0.77 eV at 80 K. Electroluminescence investigations at room temperature at both materials exhibit extended defect structures such as grain boundaries. Furthermore, it can be concluded that electroluminescence imaging in reverse bias mode indicate on serious breakdown points in solar cells, which can lead to destruction of solar cells and modules. By comparing defect-related and reverse bias electroluminescence images, a difference in the spatial distribution of defects emitting D1 radiation and defects emitting light under reverse bias beyond -12 V is detectable. In addition, there seems to be a correlation in the distribution of non-doping impurities and photoluminescence. Concerning this, vertical slabs of two silicon blocks were examined by means of Fourier-transform infrared spectroscopy and photoluminescence. A correlation of the distributions of interstitial oxygen and the band-to-band luminescence profiles could be found. Additionally, a correlation between D3/D4 luminescence profile and nitrogen distribution in the blocks was observed. Finally, the growth process, particularly the transition from amorphous to microcrystalline silicon by PECVD, was studied by combined photoluminescence and Raman investigations. Formation of silicon nano-grains was detected by means of photoluminescence and Raman spectroscopy.}, subject = {Silicon; Defects; Photoluminescence; Luminescence imaging; Silicon thin films; Silizium; Defekte; Photolumineszenz; Lumineszenz-Imaging; Silizium-D{\"u}nnfilme; Silicium; D{\"u}nnschichttechnik; Solarzelle; Fehleranalyse}, language = {en} } @phdthesis{Costache2006, author = {Costache, Florenta}, title = {Dynamics of ultra-short laser pulse interaction with solids at the origin of nanoscale surface modification}, isbn = {978-3-8322-6465-9}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-3674}, school = {BTU Cottbus - Senftenberg}, year = {2006}, abstract = {This thesis addresses fundamental physical processes which take place at the surface region of a target during and after the interaction with ultra-short laser pulses. The general goal is to bring together different phenomena and discuss the non-equilibrium nature of the interaction of femtosecond laser pulses (tp < 100 fs) with various materials, in particular dielectrics and semiconductors. Different experiments, using various techniques, are designed to explore the basic mechanisms of laser ionization, defect creation, electron-lattice energetic transfer, charged particles desorption, optical breakdown, phase transformations and surface morphological changes. Such processes are shown to depend strongly on the laser intensity. Thus, they are analyzed for intensities over four orders of magnitude (10^11-10^14 W/cm2), around the surface optical breakdown (damage) threshold intensity. First, experimental studies using time-of-flight mass spectrometry indicate that non-resonant intense ultra-short laser pulses can efficiently ionize a dielectric (semiconducting) material leading to emission of electrons as well as charged particles, i.e. atomic ions and large clusters, and neutral particles. Under these irradiation conditions, the ionization processes can be at best described by multiphoton ionization and ionization at defects sites. The structural defects provide the means for an increased positive ion desorption rate. A multiple pulse incubation effect in the ion yield can be well related with the reduction of the multi-pulse damage threshold with increasing intensity. Following the initial electron excitation and emission, positive ions are released from the surface in a substantial amount with high ion velocities indicative of a localized microscopic electrostatic expulsion. With increasing intensity, the amount of ions gets larger and larger and their velocity distribution exhibits a bimodal structure. Also, in these conditions, negative ions are detected. The ion desorption can arise from a combination of a localized electrostatic repulsion (macroscopic Coulomb explosion) and a thermal 'explosive' mechanism. The later becomes more important with increasing intensity. The very fast energy input and particle emission result in a transient perturbation and deformation of the target lattice. Using pump-probe experiments the temporal evolution of lattice dynamics can be analyzed upon single-pulse excitation for many different target materials. This deformation is indicated to be a material characteristic. It is associated with the generation of transient defects in dielectrics or fast phase transitions in semiconductors and metals. Therefore, it could well give estimates of lifetime of transient defect states or electron-phonon relaxation times.At last the surface morphology after ablation is analyzed, with emphasis on the laser-induced surface periodic patterns (ripples). The patterns observed appear to be very different from the 'classical' ripples formed after long pulse ablation. They can have periods much smaller than the incident wavelength and are rather insensitive to the variation of the laser wavelength and angle of incidence. We show that control factors are laser beam polarization and the irradiation dose. Additionally, the patterns exhibit features pointing toward a chaotic origin. Their possible formation mechanism is likely linked with the non-equilibrium nature of the interaction.}, subject = {Ultrakurzer Lichtimpuls; Nanostruktur; Oberfl{\"a}chenstruktur; Ultra-kurze Laser Pulse; Flugzeit-Massenspektrometrie; Teilchen-Emission; Ultraschnelle Gitterdynamik; Ripples; Femtosecond laser pulses; Time-of-Flight mass spectrometry; Particle emission kinetics; Ultrafast lattice dynamics; Ripples}, language = {en} }