Im ersten Teil der vorliegenden Arbeit wird der Einfluss der Abscheideparamter von In2S3 Dünnfilmen, die mittels thermischem Verdampfen hergestellt wurden, auf ihre physikalischen Eigenschaften untersucht. Es zeigte sich, dass die Abscheideparameter einen starken Einfluss auf die Oberflächenmorphologie und die strukturellen Eigenschaften haben. Durch eine Optimierung der Herstellungsparameter konnten β-In2S3 Dünnfilme in (103) Orientierung hergestellt werden. Epitaktisches Wachstum von In2S3 Schichten mit jeweils zwei bzw. vier Rotationsdomainen wurden auf c- und a-Saphir erreicht. Die fundamentale optische Bandlücke wurde für alle Dünnfilme zu 2.1 eV bestimmt. Eine starke persistente Photoleitung, welche auf tiefe Defekte innerhalb der Bandlücke zurückgeführt werden konnte, wurde unabhängig von den Abscheideparametern und dem gewählten Substrat beobachtet. Prototypen für Solarzellen wurden aus n-In2S3 und p-Zinkkobaltoxid (ZCO) hergestellt und zeigen ein hohes Sperrverhältniss und photovoltaische Aktivität, welche jedoch durch Absorption im ZCO limitiert wird. Im zweiten Teil der Arbeit wurden In2S3:V Dünnfilme ohne bzw. mit Saat- und Pufferschichten hergestellt, um deren physikalische Eigenschaften zu untersuchen bzw. um Zwischenbandsolarzellen herzustellen. Ein großer Dotierbereich von bis zu 11.4 at-% V, wurde durch einen kombinatorischer Ansatz erziehlt. Für Dünnfilme ohne Saatschicht wurde die Löslichkeitsgrenze von Vanadium in In2S3 zu 3.2 at-% V (auf Saphirsubstraten) bzw. 5.4 at-% V (auf Glassubstraten) bestimmt. Durch die Verwendung einer Saatschicht konnte die In2S3 β-Phase stabilisiert und darüber hinaus die Ausbildung von Fremdphasen unterdrückt werden. In2S3:V Dünnfilme mit über 5.8 at-% V auf Saphirsubstraten zeigten bei Raumtemperatur p-Typ Leitfähigkeit. Für Temperaturen unterhalb einer kritischen Temperatur ergab sich ein Wechsel von p- zu n-Leitung. Darüber hinaus sank die Mobilität dieser Schichten unterhalb der kritischen Temperatur signifikant ab. Die Ladungsträgerdichte blieb jedoch über den gesamte Temperaturbereich hinweg konstant und war mit Werten im Bereich von 1022 cm−3 zudem sehr hoch. Diese elektrischen Eigenschaften sind sehr untypisch für einen gewöhnlichen Halbleiter. Sie konnten jedoch im Rahmen dieser Arbeit durch das Modell der Zwischenbandsolarzelle beschieben werden. Als Schlussfolgerung dessen, wurde die Vanadiumkonzentration, bei der sich das Zwischenband ausbildet zu 3.2 at-% V bestimmt. Da sich herausstellte, das In2S3:V bei Raumtemperatur p-Typ ist, konnten keine Zwischenbandsolarzellen mit p-ZCO hergestellt werden.:1 Introduction 1 2 Theoretical background 3 2.1 Indium sulfide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2 The physics of solar cells . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.3 The concept of intermediate band solar cells . . . . . . . . . . . . . . . 8 2.4 Indium sulfide as intermediate band material . . . . . . . . . . . . . . . 11 2.5 Charge transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.6 Electronic defect states . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3 Methods 17 3.1 Growth and structuring techniques . . . . . . . . . . . . . . . . . . . . 17 3.1.1 Thermal evaporation . . . . . . . . . . . . . . . . . . . . . . . . 17 3.1.2 Pulsed laser deposition . . . . . . . . . . . . . . . . . . . . . . . 19 3.1.3 Sputter deposition . . . . . . . . . . . . . . . . . . . . . . . . . 20 3.1.4 Photolithography . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.2 characterization techniques . . . . . . . . . . . . . . . . . . . . . . . . . 22 3.2.1 X-ray diffraction measurement . . . . . . . . . . . . . . . . . . . 22 3.2.2 Hall effect measurement . . . . . . . . . . . . . . . . . . . . . . 23 3.2.3 Current-voltage measurement . . . . . . . . . . . . . . . . . . . 25 3.2.4 Temperature-dependent current-voltage measurement . . . . . . 26 3.2.5 Resistance measurement . . . . . . . . . . . . . . . . . . . . . . 26 3.2.6 Spectroscopic ellipsometry . . . . . . . . . . . . . . . . . . . . . 26 3.2.7 Energy dispersive X-ray spectroscopy . . . . . . . . . . . . . . . 27 3.2.8 Transmittance and reflection spectroscopy . . . . . . . . . . . . 27 4 Physical properties of undoped In2S3 . . . . . . . . . .29 4.1 Impact of the growth parameters on the composition . . . . . . . . . . 31 4.2 Desorption mechanisms and their influence on the growth rates . . . . . 33 4.3 Surface morphological properties . . . . . . . . . . . . . . . . . . . . . 35 4.4 Structural properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 4.5 Optical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 4.5.1 Dielectric function and absorption coefficient of In2S3 . . . . . . 43 4.5.2 Impact of the growth parameter . . . . . . . . . . . . . . . . . . 48 4.5.3 Impact of the composition . . . . . . . . . . . . . . . . . . . . . 49 4.5.4 Impact of the substrate crystallinity . . . . . . . . . . . . . . . . 51 4.6 Electrical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 4.6.1 Persistent photoconductivity . . . . . . . . . . . . . . . . . . . . 52 4.6.2 Temperature dependent resistivity and Hall effect measurements 63 4.7 Device characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 4.7.1 Impact of the growth parameter . . . . . . . . . . . . . . . . . . 70 4.7.2 Impact of the substrate crystallinity . . . . . . . . . . . . . . . . 79 4.8 Solar cell performance . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 4.8.1 Impact of the growth parameter . . . . . . . . . . . . . . . . . . 83 4.8.2 Impact of the substrate crystallinity . . . . . . . . . . . . . . . . 88 5 Physical properties of vanadium-doped In2S3. . . . . . . . . .91 5.1 Vanadium incorporation into the In2S3 thin films . . . . . . . . . . . . 93 5.2 Surface morphological properties . . . . . . . . . . . . . . . . . . . . . 95 5.3 Structural properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 5.4 Optical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 5.5 Electrical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 5.6 Device characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 6 Summary and Outlook . . . . . . . . . .125 List of Abbreviations. . . . . . . . . . 131 List of Symbols. . . . . . . . . . 133 Bibliography . . . . . . . . . .137 List of Own and Contributed Articles . . . . . . . . . .149 Appendix . . . . . . . . . .151 Publikationsliste nach Promotionsordnung § 11(3). . . . . . . . . . 161 Zusammenfassung nach Promotionsordnung § 11(4) . . . . . . . . . .163 / In the first part of the presented work the influence of the growth parameter of In2S3 thin films, grown by physical vapor deposition, on their physical properties is investigated. The deposition parameters were found to have a strong influence on the surface morphology and the structural properties. By choosing appropriate deposition parameters β-phase In2S3 with a pure (103) orientation was achieved. Epitaxial growth with 2 and 4 rotational domains could be induced using c- and a-plane sapphire, respectively. The fundamental optical bandgap was determined to be direct with an energy of 2.1 eV for all In2S3 thin films. A strong persistent photoconductivity, which was attributed to deep defects within the bandgap, was observed for all In2S3 thin films independent of the preparation conditions and independent of the kind of substrate. Solar cells of n-In2S3/p-zinc-cobalt-oxide (ZCO) exhibit high current rectifications and photovoltaic activity but suffer from absorption in the ZCO layer. To study the physical properties of In2S3:V thin films and to implement intermediate band solar cells (IBSC) In2S3:V thin films without and with seed and buffer layers were fabricated, respectively. Using a combinatorial material synthesis approach doping concentrations of up to 11.4 at-% V were achieved. Thin films without seed layers exhibit a solubility limit of vanadium of 3.2 at-% V and 5.4 at-% V for thin films on sapphire and glass substrates, respectively. The In2S3:V β-phase could be stabilized and the formation of secondary phases suppresed by inserting a seed layer. A change of the type of the charge carriers from p-type at room temperature to n-type at low temperatures was observed for thin films with doping concentrations above 5.8 at-% V on sapphire substrates. Furthermore, the mobility decreases significantly below the critical temperature. Contrarily, a very high charge carrier concentration was observed independent of the temperature. This behavior, which is untypical for conventional semiconductors, could be described using the intermediate band (IB) model. According to the results of this work and the IB model, one can conclude, that above a vanadium concentration 3.2 at-% V an IB has formed. Due to the p-type conductivity of In2S3:V thin films at room temperature, rectifying IBSCs could not be implemented using p-type ZCO. Therefore, it should be replaced by an n-type material in future investigations.:1 Introduction 1 2 Theoretical background 3 2.1 Indium sulfide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2 The physics of solar cells . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.3 The concept of intermediate band solar cells . . . . . . . . . . . . . . . 8 2.4 Indium sulfide as intermediate band material . . . . . . . . . . . . . . . 11 2.5 Charge transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.6 Electronic defect states . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3 Methods 17 3.1 Growth and structuring techniques . . . . . . . . . . . . . . . . . . . . 17 3.1.1 Thermal evaporation . . . . . . . . . . . . . . . . . . . . . . . . 17 3.1.2 Pulsed laser deposition . . . . . . . . . . . . . . . . . . . . . . . 19 3.1.3 Sputter deposition . . . . . . . . . . . . . . . . . . . . . . . . . 20 3.1.4 Photolithography . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.2 characterization techniques . . . . . . . . . . . . . . . . . . . . . . . . . 22 3.2.1 X-ray diffraction measurement . . . . . . . . . . . . . . . . . . . 22 3.2.2 Hall effect measurement . . . . . . . . . . . . . . . . . . . . . . 23 3.2.3 Current-voltage measurement . . . . . . . . . . . . . . . . . . . 25 3.2.4 Temperature-dependent current-voltage measurement . . . . . . 26 3.2.5 Resistance measurement . . . . . . . . . . . . . . . . . . . . . . 26 3.2.6 Spectroscopic ellipsometry . . . . . . . . . . . . . . . . . . . . . 26 3.2.7 Energy dispersive X-ray spectroscopy . . . . . . . . . . . . . . . 27 3.2.8 Transmittance and reflection spectroscopy . . . . . . . . . . . . 27 4 Physical properties of undoped In2S3 . . . . . . . . . .29 4.1 Impact of the growth parameters on the composition . . . . . . . . . . 31 4.2 Desorption mechanisms and their influence on the growth rates . . . . . 33 4.3 Surface morphological properties . . . . . . . . . . . . . . . . . . . . . 35 4.4 Structural properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 4.5 Optical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 4.5.1 Dielectric function and absorption coefficient of In2S3 . . . . . . 43 4.5.2 Impact of the growth parameter . . . . . . . . . . . . . . . . . . 48 4.5.3 Impact of the composition . . . . . . . . . . . . . . . . . . . . . 49 4.5.4 Impact of the substrate crystallinity . . . . . . . . . . . . . . . . 51 4.6 Electrical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 4.6.1 Persistent photoconductivity . . . . . . . . . . . . . . . . . . . . 52 4.6.2 Temperature dependent resistivity and Hall effect measurements 63 4.7 Device characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 4.7.1 Impact of the growth parameter . . . . . . . . . . . . . . . . . . 70 4.7.2 Impact of the substrate crystallinity . . . . . . . . . . . . . . . . 79 4.8 Solar cell performance . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 4.8.1 Impact of the growth parameter . . . . . . . . . . . . . . . . . . 83 4.8.2 Impact of the substrate crystallinity . . . . . . . . . . . . . . . . 88 5 Physical properties of vanadium-doped In2S3. . . . . . . . . .91 5.1 Vanadium incorporation into the In2S3 thin films . . . . . . . . . . . . 93 5.2 Surface morphological properties . . . . . . . . . . . . . . . . . . . . . 95 5.3 Structural properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 5.4 Optical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 5.5 Electrical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 5.6 Device characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 6 Summary and Outlook . . . . . . . . . .125 List of Abbreviations. . . . . . . . . . 131 List of Symbols. . . . . . . . . . 133 Bibliography . . . . . . . . . .137 List of Own and Contributed Articles . . . . . . . . . .149 Appendix . . . . . . . . . .151 Publikationsliste nach Promotionsordnung § 11(3). . . . . . . . . . 161 Zusammenfassung nach Promotionsordnung § 11(4) . . . . . . . . . .163

Es werden neue Erkenntnisse über Borphosphat und Borophosphate der Haupt- und Nebengruppenmetalle vorgestellt. Neben Hydrothermalsynthesen und Feststoffreationen, die üblicherweise zur Synthese von Borophosphaten angewendet werden, haben insbesondere die solvothermalen Experimente mit Alkoholen bzw. Alkohol-Wasser-Mischungen zu neuen Ergebnissen geführt. Es wurden neue Borophosphate und Borat-Phosphate in den Systemen MxOy–B2O3–P2O5(–H2O) (M = K+, Rb+, Mg2+, Sc3+, Pr3+, Sm3+, In3+) dargestellt, weitere Verbindungen enthalten neben Mg2+ weitere Kationen der Haupt- und Nebengruppenmetalle (Ca, Sr, Ba, Mn, Fe, Co, Zn). Darüberhinaus gelang die Darstellung bislang unbekannter Scandium- und Lanthanphosphate(III) sowie von sauren Alkalimetall-Scandiumphosphaten(V). Aus Synthesen in Gegenwart von Ethylendiamin und Diazabizyklooktan wurden ferner zwei neue templatierte Scandiumphosphate mit porösen Gerüststrukturen erhalten. Die Kristallstrukturen aller Verbindungem wurden rötgenographisch anhand von Einkristallaufnahmen oder Pulverdaten aufgeklärt. Die Charakterisierung der Präparate erfolgte mit Röntgenpulverdiffraktometrie, EDX- und Elementaranalysen sowie durch Schwingungsspektroskopie und thermische Stabilitätsuntersuchungen. Zur Klassifizierung von (Metallo)borophosphaten wird eine Struktursystematik vorgeschlagen, welche Borophosphate und Metalloborophosphate entsprechend ihrer anionischen Teilstrukturen hierarchisch klassifiziert und in Analogie zur Terminologie der Silikate (nach Liebau) beschreibt. In Anlehnung an bestehende Konzepte für Boratminerale geht das Klassifizierungsschema dabei von einfachen Oligomeren aus. In einer struktursystematischen Übersicht wurden alle bis dato bekannten (Metallo)Borophosphate hierarchisch klassifiziert und sind in einer Übersicht vorgestellt. Beobachtete Verknüpfungsregeln und der Einfluss der Zusammensetzung B:P auf die Dimensionalität und die Verknüpfungsmuster der anionischen Teilstruktur werden diskutiert.

No description available.

Ternary luminescent copper and silver indium sulfide quantum dots (QDs) can be an attractive alternative to cadmium and lead chalcogenide QDs. The optical properties of Cu–In–S and Ag–In–S (AIS) QDs vary over a broad range depending on the QD composition and size. The implementation of ternary QDs as emitters in bio-sensing applications can be boosted by the development of mild and reproducible syntheses directly in aqueous solutions as well as the methods of shifting the photoluminescence (PL) bands of such QDs as far as possible into the near IR spectral range. In the present work, the copper-doping of aqueous non-stoichiometric AIS QDs was found to result in a red shift of the PL band maximum from around 630 nm to ∼780 nm and PL quenching. The deposition of a ZnS shell results in PL intensity recovery with the highest quantum yield of 15%, with almost not change in the PL band position, opposite to the undoped AIS QDs. Size-selective precipitation using 2-propanol as a non-solvent allows discrimination of up to 9 fractions of Cu-doped AIS/ZnS QDs with the average sizes in the fractions varying from around 3 to 2 nm and smaller and with reasonably the same composition irrespective of the QD size. The decrease of the average QD size results in a blue PL shift yielding a series of bright luminophors with the emission color varies from deep-red to bluish-green and the PL efficiency increases from 11% for the first fraction to up to 58% for the smallest Cu-doped AIS/ZnS QDs. The rate constant of the radiative recombination of the size-selected Cu-doped AIS/ZnS QDs revealed a steady growth with the QD size decrease as a result of the size-dependent enhancement of the spatial exciton confinement. The copper doping was found to result in an enhancement of the photoelectrochemical activity of CAIS/ZnS QDs introduced as spectral sensitizers of mesoporous titania photoanodes of liquid-junction solar cells.

Recently, there has been a growing interest in semiconductor and semiconducting oxide nanowires for applications in electronics, energy conversion, energy storage and optoelectronic devices such as field effect transistors, solar cells, Li- ion batteries, gas sensors, light emitting diodes, field emission displays etc. Semiconductor and semiconducting oxide nanowires have been synthesized widely by different vapor transport methods. However, conditions like high growth temperature, low vacuum, carrier gases for the growth of nanowires, limit the applicability of the processes for the growth of nanowires on a large scale for different applications. In this thesis work, studies have been made on the growth of semiconductor and semiconducting oxide nanowires at a relatively lower substrate temperature (< 500 °C), in a high vacuum (1× 10-5 mbar), without employing any carrier gas, by electron beam and resistive thermal evaporation processes. The morphology, microstructure, and composition of the nanowires have been investigated using analytical techniques such as SEM, EDX, XRD, XPS, and TEM. The optical properties of the films such as reflectance, transmittance in the UV-visible and near IR region were studied using a spectrophotometer. Germanium nanowires were grown at a relatively lower substrate temperature of 380-450 °C on Si substrates by electron beam evaporation (EBE) process using a Au-assisted Vapor-Liquid-Solid mechanism. High purity Ge was evaporated in a high vacuum of 1× 10-5 mbar, and gold catalyst coated substrates maintained at a temperature of 380-450 °C resulted in the growth of germanium nanowires via Au-catalyzed VLS growth. The influence of deposition parameters such as the growth temperature, Ge evaporation rate, growth duration, and gold catalyst layer thickness has been investigated. The structural, morphological and compositional studies have shown that the grown nanowires were single-crystalline in nature and free from impurities. The growth mechanism of Germanium nanowires by EBE has been discussed. Studies were also made on Silicon nanowire growth with Indium and Bismuth as catalysts by electron beam evaporation. For the first time, silicon nanowires were grown with alternative catalysts by the e-beam evaporation method. The use of alternative catalysts such as Indium and Bismuth results in the decrease of nanowire growth temperature compared to Au catalyzed Si nanowire growth. The doping of the silicon nanowires is possible with an alternative catalyst. The second part of the thesis concerns the growth of oxide semiconductors such as SnO2, Sn doped Indium oxide (ITO) nanowires by the electron beam evaporation method. For the first time, SnO2 nanowires were grown with a Au-assisted VLS mechanism by the electron beam evaporation method at a low substrate temperature of 450 °C. SEM, XRD, XPS, TEM, EDS studies on the grown nanowires showed that they were single crystalline in nature and free of impurities. The influence of deposition parameters such as the growth temperature, oxygen partial pressure, evaporation rate of Sn, and the growth duration has been investigated. Studies were also done on the application of SnO2 nanowire films for UV light detection. ITO nanowires were grown via a self-catalytic VLS growth mechanism by electron beam evaporation without the use of any catalyst at a low substrate temperature of 250-400 °C. The influence of deposition parameters such as the growth temperature, oxygen partial pressure, evaporation rate of ITO, and growth duration has been investigated. Preliminary studies have been done on the application of ITO nanowire films for transparent conducting coatings as well as for antireflection coatings. The final part of the work is on the Au-assisted and self catalytic growth of SnO2 and In2O3 nanowires on Si substrates by resistive thermal evaporation. For the first time, SnO2 nanowires were grown with a Au-assisted VLS mechanism by the resistive thermal evaporation method at a low substrate temperature of 450 °C. SEM, XRD, XPS, TEM, and EDS studies on the grown nanowires showed that they were single crystalline in nature and free of impurities. Studies were also made on the application of SnO2 nanowire films for methanol sensing. The self-catalytic growth of SnO2 and In2O3 nanowires were deposited in high vacuum (5×10-5 mbar) by thermal evaporation using a modified evaporation source and a substrate arrangement. With this arrangement, branched SnO2 and In2O3 nanowires were grown on a Si substrate. The influence of deposition parameters such as the applied current to the evaporation boat, and oxygen partial pressure has been investigated. The growth mechanism behind the formation of the branched nanowires as well as nanowires has been explained on the basis of a self-catalytic vapor-liquid-solid growth mechanism. The highlight of this thesis work is employing e-beam evaporation and resistive thermal evaporation methods for nanowire growth at low substrate temperatures of ~ 300-500 °C. The grown nanowires were tested for applications such as gas sensing, transparent conducting coatings, UV light detection and antireflection coating etc. The thesis is divided into nine chapters and each of its content is briefly described below. Chapter 1 In this chapter, a brief introduction is given on nanomaterials and their applications. This chapter also gives an overview of the different techniques and different growth mechanisms used for nanowires growth. A brief overview of the applications of semiconductors and semiconductor oxide nanowires synthesized is also presented. Chapter 2 Different experimental techniques employed for the growth of Si, Ge, SnO2, In2O3, ITO nanowires have been described in detail in this chapter. Further, the details of the different techniques employed for the characterization of the grown nanowires were also presented. Chapter 3 In this chapter, studies on the growth of Germanium nanowires by electron beam evaporation (EBE) are given. The influence of deposition parameters such as growth temperature, evaporation rate of germanium, growth duration, and catalyst layer thickness was investigated. The morphology, structure, and composition of the nanowires were investigated by XRD, SEM, and TEM. The VLS growth mechanism has been discussed for the formation of the germanium nanowires by EBE using Au as a catalyst. Chapter 4 This chapter discusses the growth of Si nanowires with Indium and Bismuth as an alternate to Au-catalyst by electron beam evaporation. The influence of deposition parameters such as growth temperature, Si evaporation rate, growth duration, and catalyst layer thickness has been investigated. The grown nanowires were characterized using XRD, SEM, TEM and HRTEM. The Silicon nanowires growth mechanism has been discussed. Chapter 5 This chapter discusses the Au-catalyzed VLS growth of SnO2 nanowires by the electron beam evaporation method as well as Antimony doped SnO2 nanowires by co-evaporation method at a low substrate temperature of 450 °C. The grown nanowires were characterized using XRD, SEM, TEM, STEM, Elemental mapping, HRTEM, and XPS. The effect of deposition parameters such as oxygen partial pressure, growth temperature, catalyst layer thickness, evaporation rate of Sn, and the growth duration of nanowires were investigated. The SnO2 nanowires growth mechanism has been explained. Preliminary studies were made on the possible use of pure SnO2 and doped SnO2 nanowire films for UV light detection. SnO2 nanowire growth on different substrates such as stainless steel foil (SS), carbon nanosheets films, and graphene oxide films were studied. SnO2 nanowire growth on different substrates, especially SS foil will be useful for Li-ion battery applications. Chapter 6 This chapter discusses the self catalyzed VLS growth of Sn doped Indium oxide (ITO) nanowires by the electron beam evaporation method at a low temperature of 250-400 °C. The grown nanowires were characterized using XRD, SEM, TEM, STEM, HRTEM, and XPS. The effect of deposition parameters such as oxygen partial pressure, growth temperature, evaporation rate of ITO, and the growth duration of the nanowires were investigated. Preliminary studies were also made on the possible use of self-catalyzed ITO nanowire films for transparent conducting oxides and antireflection coatings. ITO nanowire growth on different and large area substrates such as stainless steel foil (SS), and Glass was done successfully. ITO nanowire growth on different substrates, especially large area glass substrates will be useful for optoelectronic devices. Chapter 7 In this chapter, studies on the growth of SnO2 nanowires by a cost-effective resistive thermal evaporation method at a relatively lower substrate temperature of 450 °C are presented. The grown nanowires were characterized using XRD, SEM, TEM, HRTEM, and XPS. Preliminary studies were done on the possible use of SnO2 nanowire films for methanol sensing. Chapter 8 This chapter discusses the self-catalytic growth of SnO2 and In2O3 nanowires by resistive thermal evaporation. The nanowires of SnO2 and In2O3 were grown at low temperatures by resistive thermal evaporation using a modified source and substrate arrangement. In this arrangement, branched SnO2 nanowires, and In2O3 nanowires growth was observed. The grown nanowires were characterized using XRD, SEM, TEM, HRTEM, and XPS. The possible growth mechanism for branched nanowires growth has been explained. Chapter 9 The significant results obtained in the present thesis work have been summarized in this chapter.

Currently conventional sources like coal, petroleum and natural gas meet the energy requirements of developing and undeveloped countries. Over a period of time there is high risk of these energy sources getting depleted. Hence an alternate source of energy i.e. renewable energy is the need of the hour. The advantages of renewable energy like higher sustainability, lesser maintenance, low cost of operation, and minimal impact on the environment make the role of renewable energy sources significant. Out of the various renewable energy sources like solar energy, wind energy, hydropower, biogas, tidal and geothermal, usage of solar energy is gradually increasing. Among various solar energy sources, Photovoltaics has dominated over the past two decades since it is free clean energy and availability of abundant sunlight on earth. Over the past few decades, thin film solar cells (TFSC) have gained considerable interest as an economically feasible alternative to conventional silicon (Si) photovoltaic devices. TFSCs have the potential to be as efficient as Si solar cells both in terms of conversion efficiency as well as cost. The advantages of TFSC are that they are easy to prepare, lesser thickness, requires lesser materials, light weight, low cost and opto-electronic properties can be tuned by varying the process parameters. The present study is focused on the fabrication of AgInS2/ZnS heterojunction thin film solar cell. AgInS2 absorber layer is deposited using both vacuum (sputtering/sulfurization) and non-vacuum (ultrasonic spray pyrolysis) techniques. ZnS window layer is prepared using thermal evaporation technique, detailed experimental investigation has been conducted and the results have been reported in this work. The thesis is divided into 6 chapters. Chapter 1 gives general introduction about solar cells and working principle of solar cell. It also discusses thin film solar cell technology and its advantages. Layers of thin film solar cell structure, Significance of each layers and possible materials to be used are emphasized. A detailed overview of the available literature on both AgInS2 absorber layer and ZnS window layer has been presented. Based on the literature review, objectives of the present work are defined. Chapter 2 explains the theory and experimental details of deposition techniques used for the growth of AgInS2 and ZnS films. Details of characterization techniques to study film properties are described in detail. Chapter 3 presents a systematic study of AgInS2 thin films deposited by sulfurization of sputtered Ag-In metallic precursors. Initially, AgInS2 films are deposited by varying the substrate temperature and properties of as-deposited films are characterized. Structural, morphological, electrical and optical properties of AgInS2 films are explained. From these studies, samples with better properties at particular substrate temperature are optimized. By fixing the substrate temperature, deposition time of silver is varied by keeping other deposition conditions same and the properties of films are discussed. It was observed that deposition time of silver doesn’t have much impact on structural properties of AgInS2 films. However, opto-electric properties of AgInS2 films are enhanced. Based on characterization studies, deposition time of silver is optimized. Deposition time of indium is varied by keeping substrate temperature and silver deposition to optimized value. The properties of as-deposited films are discussed. Based on the above studies, the optimized p type films have a band gap of 1.64 eV, carrier concentration of 1013 ions/cm3 and Resistivity of order 103 Ω-cm. Chapter 4 presents a systematic study of AgInS2 thin films deposited by ultrasonic spray pyrolysis. AgInS2 films are deposited by varying the substrate temperature and properties of as deposited films are characterized. Structural, morphological, electrical and optical properties of AgInS2 films are explained. From these studies, samples with better properties at particular substrate temperature are optimized. By fixing the substrate temperature, concentration of silver molarity in the precursor solution is varied by keeping other deposition conditions same and the properties of films are discussed. Structural, optical and electrical properties of AgInS2 films are enhanced with the increase in silver concentration. Based on characterization studies, concentration of silver is optimized. Similarly concentration of indium molarity in the precursor solution is varied and the properties of as-deposited films are discussed. Finally, sulfur molarity in the precursor solution is varied and properties of films are discussed. It was observed that increasing sulfur after certain limit does not have any effect on the properties of the films. Based on the above studies, this method resulted in the films with resistivity of 103 Ω-cm and band gap of 1.64 eV. These films showed a carrier concentration of 1013 ions/cm3. Chapter 5 describes the growth of ZnS films using thermal evaporation technique. Influence of thickness on the properties of ZnS films is explained. Samples with good crystallinity, high transmission, and wider gap are selected for device fabrication. This p type layer showed a band gap of 3.52 eV. Solar cells have been fabricated using the AgInS2 films developed by both sputtering and ultrasonic spray pyrolysis techniques. A maximum cell efficiency of 0.92 percent has been achieved for the cell with 0.950 µm thick sputtered AgInS2 layer and thermally evaporated 42 nm thick ZnS layer. In comparison, the ultrasonic spray pyrolysis deposited films gave an efficiency of 0.54 percent. These values are comparable to those mentioned in a couple of reports earlier. Chapter 6 summarizes the conclusions drawn from the present investigations and scope of future work is suggested.

Ternary luminescent copper and silver indium sulfide quantum dots (QDs) can be an attractive alternative to cadmium and lead chalcogenide QDs. The optical properties of Cu–In–S and Ag–In–S (AIS) QDs vary over a broad range depending on the QD composition and size. The implementation of ternary QDs as emitters in bio-sensing applications can be boosted by the development of mild and reproducible syntheses directly in aqueous solutions as well as the methods of shifting the photoluminescence (PL) bands of such QDs as far as possible into the near IR spectral range. In the present work, the copper-doping of aqueous non-stoichiometric AIS QDs was found to result in a red shift of the PL band maximum from around 630 nm to ∼780 nm and PL quenching. The deposition of a ZnS shell results in PL intensity recovery with the highest quantum yield of 15%, with almost not change in the PL band position, opposite to the undoped AIS QDs. Size-selective precipitation using 2-propanol as a non-solvent allows discrimination of up to 9 fractions of Cu-doped AIS/ZnS QDs with the average sizes in the fractions varying from around 3 to 2 nm and smaller and with reasonably the same composition irrespective of the QD size. The decrease of the average QD size results in a blue PL shift yielding a series of bright luminophors with the emission color varies from deep-red to bluish-green and the PL efficiency increases from 11% for the first fraction to up to 58% for the smallest Cu-doped AIS/ZnS QDs. The rate constant of the radiative recombination of the size-selected Cu-doped AIS/ZnS QDs revealed a steady growth with the QD size decrease as a result of the size-dependent enhancement of the spatial exciton confinement. The copper doping was found to result in an enhancement of the photoelectrochemical activity of CAIS/ZnS QDs introduced as spectral sensitizers of mesoporous titania photoanodes of liquid-junction solar cells.

Es werden neue Erkenntnisse über Borphosphat und Borophosphate der Haupt- und Nebengruppenmetalle vorgestellt. Neben Hydrothermalsynthesen und Feststoffreationen, die üblicherweise zur Synthese von Borophosphaten angewendet werden, haben insbesondere die solvothermalen Experimente mit Alkoholen bzw. Alkohol-Wasser-Mischungen zu neuen Ergebnissen geführt. Es wurden neue Borophosphate und Borat-Phosphate in den Systemen MxOy–B2O3–P2O5(–H2O) (M = K+, Rb+, Mg2+, Sc3+, Pr3+, Sm3+, In3+) dargestellt, weitere Verbindungen enthalten neben Mg2+ weitere Kationen der Haupt- und Nebengruppenmetalle (Ca, Sr, Ba, Mn, Fe, Co, Zn). Darüberhinaus gelang die Darstellung bislang unbekannter Scandium- und Lanthanphosphate(III) sowie von sauren Alkalimetall-Scandiumphosphaten(V). Aus Synthesen in Gegenwart von Ethylendiamin und Diazabizyklooktan wurden ferner zwei neue templatierte Scandiumphosphate mit porösen Gerüststrukturen erhalten. Die Kristallstrukturen aller Verbindungem wurden rötgenographisch anhand von Einkristallaufnahmen oder Pulverdaten aufgeklärt. Die Charakterisierung der Präparate erfolgte mit Röntgenpulverdiffraktometrie, EDX- und Elementaranalysen sowie durch Schwingungsspektroskopie und thermische Stabilitätsuntersuchungen. Zur Klassifizierung von (Metallo)borophosphaten wird eine Struktursystematik vorgeschlagen, welche Borophosphate und Metalloborophosphate entsprechend ihrer anionischen Teilstrukturen hierarchisch klassifiziert und in Analogie zur Terminologie der Silikate (nach Liebau) beschreibt. In Anlehnung an bestehende Konzepte für Boratminerale geht das Klassifizierungsschema dabei von einfachen Oligomeren aus. In einer struktursystematischen Übersicht wurden alle bis dato bekannten (Metallo)Borophosphate hierarchisch klassifiziert und sind in einer Übersicht vorgestellt. Beobachtete Verknüpfungsregeln und der Einfluss der Zusammensetzung B:P auf die Dimensionalität und die Verknüpfungsmuster der anionischen Teilstruktur werden diskutiert.

Nous avons élaboré des structures de quatre couches d'InN/InP (100) en enrichissant en In la surface nitrurée à l'aide d'une cellule d'évaporation calibrée. Les propriétés physiques de ces structures ont été étudiées in-situ à l'aide de spectroscopie, des électrons Auger (AES), des photoélectrons X (XPS) et UV (UPS) avant d'être analysées ex-situ par photoluminescence (PL) et mesures électriques (I(V) et C(V)). Nous avons mené une étude de PL en fonction de la température et l'évolution de l'énergie du pic de PL obtenue en fonction de la température suivait la forme en S-inversé caractéristique des effets de localisation. Les caractéristiques électriques courant-tension des structures Hg/InN/InP montrent qu'elles forment un contact Schottky. Les caractéristiques capacité-tension montrent qu'elles se comportent comme une structure lorsqu'on polarise négativement et comme une structure MIS quand on polarise positivement. Dans la dernière partie de cette thèse, des résultats sont présentés sur l'étude des propriétés physico-chimiques et optiques de semi-conducteurs poreux : le GaAs et l'InP poreux. L'effet de confinement quantique dans les cristallites de GaAs poreux a été confirmé après avoir caractérisé optiquement par Photoréflectivité (PR) et photoluminescence (PL) des échantillons de GaAs poreux

Transparent conducting oxides (TCOs) combine optical transparency in the visible region with a high electrical conductivity. In2O3 doped with Sn (widely, but somewhat misleadingly, known as indium tin oxide or ITO) is at present the most important TCO, with applications in liquid crystal displays, touch screen displays, organic photovoltaics and other optoelectronic devices. Surprisingly, many of its fundamental properties have been the subject of controversy or have until recently remained unknown, including even the nature and magnitude of the bandgap. The technological importance of the material and the renewed interest in its basic physics prompted the research described in this thesis. This thesis aims (i) to establish conditions for the growth of high-quality In2O3 nanostructures and thin films by oxygen plasma assisted molecular beam epitaxy and (ii) to conduct comprehensive investigations on both the surface physics of this material and its structural and electronic properties. It was demonstrated that highly ordered In2O3 nanoislands, nanorods and thin films can be grown epitaxially on (100), (110) and (111) oriented Y-stabilized ZrO2 substrates respectively. The mismatch with this substrate is -1.7%, with the epilayer under tensile strain. On the basis of ab initio density functional theory calculations, it was concluded that the striking influence of substrate orientation on the distinctive growth modes was linked to the fact that the surface energy for the (111) surface is much lower than for either polar (100) or non-polar (110) surfaces. The growth of In2O3(111) thin films was further explored on Y-ZrO2(111) substrates by optimizing the growth temperature and film thickness. Very thin In2O3 epilayers (35 nm) grew pseudomorphically under high tensile strain, caused by the 1.7% lattice mismatch with the substrate. The strain was gradually relaxed with increasing film thickness. High-quality films with a low carrier concentration (5.0  1017 cm-3) and high mobility (73 cm2V-1s-1) were obtained in the thickest films (420 nm) after strain relaxation. The bandgap of the thinnest In2O3 films was around 0.1 eV smaller than that of the bulk material, due to reduction of bonding-antibonding interactions associated with lattice expansion. The high-quality surfaces of the (111) films allowed us to investigate various aspects of the surface structural and electronic properties. The atomic structure of In2O3 (111) surface was determined using a combination of scanning tunnelling microscopy, analysis of intensity/voltage curves in low energy electron diffraction and first-principles ab initio calculations. The (111) termination has an essentially bulk terminated (1 × 1) surface structure, with minor relaxations normal to the surface. Good agreement was found between the experimental surface structure and that derived from ab initio density functional theory calculations. This work emphasises the benefits of a multi-technique approach to determination of surface structure. The electronic properties of In2O3(111) surfaces were probed by synchrotron-based photoemission spectroscopy using photons with energies ranging from the ultraviolet (6 eV) to the hard X-ray regime (6000 eV) to excite the spectra. It has been shown that In2O3 is a highly covalent material, with significant hybridization between O and In orbitals in both the valence and the conduction bands. A pronounced electron accumulation layer presents itself at the surfaces of undoped In2O3 films with very low carrier concentrations, which results from the fact the charge neutrality level of In2O3 lies well above the conduction band minimum. The pronounced electron accumulation associated with a downward band bending in the near surface region creates a confining potential well, which causes the electrons in the conduction band become quantized into two subband states, as observed by angle resolved photoemission spectra (ARPES) Fermi surface mapping. The accumulation of high density of electrons near to the surface region was found to shrink the surface band gap through many body interactions. Finally epitaxial growth of In2O3 thin films on α-Al2O3(0001) substrates was investigated. Both the stable body centred cubic phase and the metastable hexagonal corundum In2O3 phase can be stabilized as epitaxial thin films, despite large mismatches with the substrate. The growth mode involves matching small but different integral multiples of lattice planes of the In2O3 and the substrate in a domain matching epitaxial growth mode.