SEMICONDUCTORS

Author: SOLER VILAMITJANA DAVID.
Year: 2004.
University: BARCELONA [www.ub.es].
Place of defense: FACULTAD DE FÍSICA.
Place of preparation: FACULTAD DE FÍSICA.

Summary: The production of electricity by photovoltaic conversion of solar energy has led to a power source alternative fully demonstrated from the technological point of view. The crystalline silicon is the material used for the manufacture of photovoltaic panels, but its high cost of production has led to the introduction of new technologies based on materials in thin layer. The use of photovoltaic stacked structures, which combine materials in thin layer with a different width of the forbidden band, allows better use of solar radiation reaching thus conversion efficiencies greater than simple structures. In terms of these materials stacked solar cells, the use of silicon nanocristalino (nc-Si: H) in combination with amorphous silicon (a-Si: H) is one of the most promising alternatives because of low costs production and the abundance of material. Furthermore, the combination of a-Si: Hy nc-Si: H devices leads to more stable than those obtained with simple structures of a-Si: H. The technique known as deposit growth in chemical vapor phase assisted hot filament (Hot-Wire CVD) has been analyzed at the University of Barcelona since 1993, giving rise to three dissertations so far. These studies focused on the investigation of silicon nanocristalino (nc-Si: H) and related devices, this being the first thesis work focused on the acquisition and characterization of solar cells based on a-Si: H using this technique. The use of Hot-Wire CVD presents certain advantages over other techniques commonly used deposit, as are the ability to obtain quality material at speeds of deposit or high ease of obtaining devices on large area substrates. Moreover, in our study was imposed as a condition of employment technological substrate temperatures (about 200Â ° C), allowing this fact the future use of low-cost substrates such as plastics. In 10 pages of this work examines the influence of different parameters deposit on the properties and structural optoelectrónicas of a-Si: H, both intrinsic and doped. He then discusses our first solar cells obtained exclusively by Hot-Wire CVD at low substrate temperatures. In particular, the architecture of the devices studied is known as the "superestrato" Pin, referring to the order in which the different layers are deposited on the semiconductor substrate.

Author: BLANQUE SERVANE.
Year: 2004.
University: AUTÓNOMA DE BARCELONA [www.uab.es].
Place of defense: UNIVERSITÉ MONTPELLIER FRANCIA.
Place of preparation: ESCUELA DE POSTGRADO.

Author: RACHID AYOUCHI.
Year: 2004.
University: MÁLAGA [www.uma.es].
Place of defense: FACULTAD DE CIENCIAS , UNIVERSIDAD DE MÁLAGA.
Place of preparation: FACULTAD DE CIENCIAS, UNIVERSIDAD DE MÁLAGA.

Summary: This report is divided into 6 chapters and an appendix devoted to the experimental techniques used in the characterization of materials studied in this work. - Chapter I: Picks up approach and objectives of this research work. - Chapter II: This chapter consists of a summary of the most important techniques for preparing thin films and their application in the preparation of the materials studied in this report. In the same chapter gives a detailed description of the art spray Pirólisis, including the various processes involved in the growth of thin films, as well as a brief description of the modes of growth thin layers more common. It also presents some of the variations of this method and its advantages and disadvantages. - Chapter III: Preparation and study of pure zinc oxide and doped with aluminum. It includes the results for the study of the impact of temperature on growth of the films and their influence on the structural and morphological properties. It will also discuss the influence of it on the electrical and optical properties of the films. - Chapter IV: It presents the results concerning the growth of thin films of oxides of tin SnOx and its potential as material for electrodes in lithium batteries. To that end, we have an interest in the study of gracious influence of the variation in the flow of precursor on the dissolution speeds growth of the films, as well as on the morphology and chemical composition of the deposits. Finally electrical measurements have been performed (electrochemical, and measures impedance spectroscopy HP) to determine the potential of these materials as electrodes for lithium batteries. - Chapter V: In this chapter we studied the influence of heat treatments as a follow-up to the process of deposition films, in particular, the effect of two types of thermal treatments, with a conventional ramps warming soft 5 DC / min and another quick with a ramp above 500DC/min, on the properties morphological, structural and compositional. Finally we have made steps on HP structures MFM and MFSpara assess the effects of heat treatments. - Chapter VI: This chapter presents the overall findings of this research work. - Appendix: Appendix presents in detail the theoretical foundations of the different experimental techniques used in the characterization of materials studied in this thesis.

Author: ULLOA HERRERO JOSE MARIA.
Year: 2004.
University: POLITÉCNICA DE MADRID [www.upm.es].
Place of defense: E.T.S.I. TELECOMUNICACIONES.
Place of preparation: E.T.S.I. TELECOMUNICACIONES I.S.O.M..

Summary: The work is a contribution to the development of quantum well laser diodes of InGaAs / GaAs (111) B for emission 1.06 -1.1 micron and GaInNAs / GaAs for the region of 1.3 -1.55 micron. We present a detailed theoretical study that includes the calculation of the structure of gangs and gain material referred quantum wells. In the cso of InGaAs has shown laser emission at room temperature up to 1.11 micron and shows that the field piezélectrico is only partially shielded in doorway. It is also estimated for the first time renormalización the gap in these devices, results to be higher than in the case equivalent substrate conventional (100). As to GalnNas addition to analyze and theoretically change the N produced in the structure of gangs and material gain, is a study of structural and optical quantum wells which enables the phenomenon of the localization of carriers with the morphology of the pit, and to clarify the effect of heat treatment on fotoluminiscencia. They are used diodes electroluminiscentes to demonstrate the enormous impact of recombination no-radiativa and finally showed up 1.52 micron laser emission values record densidd current threshold.

Author: ALBORNOZ JOSÉ GREGORIO.
Year: 2004.
University: AUTÓNOMA DE MADRID [www.uam.es].
Place of defense: FACULTAD DE CIENCIAS DEPARTAMENTO DE FISICA.
Place of preparation: FACULTAD DE CIENCIAS , DEPARTAMENTO DE FÍSICA APLICADA.

Summary: This is a working pilot devoted to the study of polycrystalline semiconductor alloys system quaternary Ag1-XCuXlnSe2. The most important property of these compounds is that they have the optical absorption coefficient higher among semiconductor materials that are currently available for the design of photovoltaic systems and their conductivity can be changed detipo bread according to the value of the atomic composition X. In this work we have synthesized samples. There has been an analysis of the crystalline structure, chemical composition and differential thermal analysis. There have also been identified propíedades electrical and optical at room temperature. It has been estimated the role and energy transitions of the electronic structure of the system through technical Elipsometría. The type of conductivity, energy electronic transition and network parameters (a, b) show two distinct regions of behavior for membership X values lower than 0.4 (type n) and X values greater than 0.6 (type p) . The results of the work are of great interest to the photovoltaics industry and optoelectronics.

Author: FUSTER SIGNES DAVID.
Year: 2005.
University: VALENCIA [www.uv.es].
Place of defense: FACULTAD DE FÍSICA.
Place of preparation: FACULTAD DE FISICA.

Summary: Experimental study on growth epitaxial yarn quantum auto-ensamblados arsenide Indian substrates 001, fosfuro Indianness and their optical properties. Threads quantum InAs / InP, which allows the free movement of carriers or just na dimension can be based devices poptelectrónicos working at wavelengths of technological interest. Specifically, this work has been shown a very wide tuning range, from 1300 until almost 2000nm, range of interest to telecommunications and biomedical application. They have been used situ techniques are caractización structural and morphological, to study the evolution of growth. It is also emphasize the use of optical characterization techniques of fotolumniscencia in continuous wave and it is time for the study of recombination excitónica in nanostructures InAs / InP layer multilayer simple and stacked. These results confirm the potential for application of these materials for the manufacture of laser diode in such ranges of wavelengths.

Author: Rey Mazón Miguel.
Year: 2005.
University: AUTÓNOMA DE MADRID [www.uam.es].
Place of defense: Facultad de Ciencias.
Place of preparation: Facultad de Ciencias.

Summary: This thesis finds some problems associated with the transport of cargo and heat in double quantum wells and dots, built with semiconductor heterostructures, in the presence of external voltage dependent regular time. When transportation takes place in a consistent manner, interaction with potential fields or time-dependent changes the properties of transmission through semiconductor nanostructures. For this reason, we studied the behavior of the steady stream of interest in different situations. First is the effect of control of the electric current. Choosing the parameters of voltage applied, the interaction between the wells can be modified, reaching set aside for certain values of voltage amplitude and frequency of the oscillation. The study of the consistent suppression of the flow was known in isolated systems, but their consideration in transport problems, where contact with the electrodes should be included explicitly, has been taken into account only recently. The numerical results were obtained using the formalism of dispersion (scattering) of Landauer, with modifications appropriate to deal with time-dependent systems. To calculate the transmissions have been used matrices transfer (Wagner, Phys. Rev. TO (1995) 51, 798) and formalism Floquet-Green (Kohler, Lehmann and HÃ ¤ nggi, Phys. Rep. (2005) 406 , 379). The first is a particular version of the Floquet theory in which states asintóticos of electrons are used as a flat waves. The calculations reproduced in the limit of high frequency results in an approximation of the model of strong links (tight-binding). This approach offers interesting results easier to analyze qualitatively since converting the initial problem of time dependent on a single problem of time. The temporary unit is included renormalizando parameters (acoplaimento between wells and distribution of electrons in the contacts) that influence the flow. The production of an electric current in the absence of an external potential difference is the other issue dealt with in this thesis. The application of a signal to an external structure skewed because the probability of transmission depends on the side by impacting electrons. Thus, the electric current can be pumped through the heteroestructura. This effect pumping electrons is also home quantum and can be understood with the analytical tools used for the above problem. In this case, our interest is focused on demonstrating that double quantum wells this transport is not adiabatic and takes place through the transmission tunnel helped by photons, ie interaction with the electric potential. On the other hand, one of our goals has been to consider whether the behavior of a device pumping electrons as part of a circuit can be characterized by the transmission and reflection properties of its elements. Finally, we consider the heat due to the flow of electrons in a device pumping. The formalism of Landauer can generalized once again to calculate how is the exchange of energy when the electrons pass through the double quantum well. We thought it was particularly important to investigate the conditions under which a stream of electrons can help to cool one of the electrodes. This can be achieved with a choice of the structure of energy levels in the wells and an adjustment of the frequency of potential alternate implemented. The basis of our model for cooling is based on the exchange of hot electrons, above the electrode potential chemical, cold electrons from states located across the heteroestructura. The numerical results presented confirm our hipoótesis. To check our predicci 8 ones cua 3b7 litativas, we studied how dependent heat of some variables. Among the cases of possible importance experimental heat production in the absence of electric current net is perhaps the most interesting. According to our calculations, this is possible for a wide range of temperatures in the electrodes.

Author: HERRERA CABRERA MARIA JOSE.
Year: 2005.
University: LA LAGUNA [www.ull.es].
Place of defense: FACULTAD DE FÍSICA.
Place of preparation: UNIVERSIDAD DE LA LAGUNA.

Summary: This work ab initio methods are based on the Functional Theory of the density Pseudopotenciales. It has also worked with the theory of the Disruption of the Density Functional. With these tools has been studied very different properties in different semiconductor materials to show the versatility of the methods of first principles and to highlight its importance in the study of solid semiconductors subjected to hydrostatic pressure. It has studied the sequence of structural P under pressure, presenting results that match very well with existing data, both for the parameters of the different structures of this material to the pressures of transition between them. There is a stage in that sequence structural unknown. We propose as a credible candidate to that stage structure lmmm with internal parameters v equal to 1 / 2, the same as for phase SH, but with respect b / c different. Discard other potential candidates: NaCl structures, CCB, FCC and distortions in the direction [001] of them all, HCP, NiAs and Beta-Sn. We have studied electronic properties, structural dynamics of BAs and, as such structures stable ambient pressure and high pressure, the structure of bands for each of these phrases; for phase at low pressure are studied their gaps, the variation thereof with pressure, its modules of elasticity and its variation with pressure, the criteria for mechanical stability, the relationship dispersion fonones, parameter Gruneisen, charging effective dielectric tensor, the separation of the optical modes at the point gamma, and so on. This compound present a comprotamiento anomalous in some respects over other semiconductor III-V because of the chemistry B. Moreover, it is difficult to synthesize, so there is no experimental data available many of its properties. This study is predictive in this regard, since it is the only estimate exists of their behavior under pressure for the time being. We have studied the optical properties of ZnO under pressure, in collaboration with experimental groups at the University of Valencia. We studied their energy bands at different pressures, the composition of levels of each band at points of high symmetry: determine the coefficients of pressure from the gaps and attach to the different transitions are observed in the absorption spectrum. This material in its infancy NaCl is an indirect gap semiconductor value 2.45 eV. There is a direct transition to intense energy increased (4.6 eV to 10 GPa) with a large positive pressure coefficient, and has been assigned to the transition indirect lowest point range.

Author: LOPEZ MARTINEZ ANTONIO MIGUEL.
Year: 2006.
University: POLITÉCNICA DE CATALUÑA [www.upc.edu].
Place of defense: AULA MASTER EPSEVG.
Place of preparation: C4 Jordi Girona, 1-3, campus nord 08034.

Summary: This research work has been implemented characterization of semiconductor which is based thermal power structure developed with Skutterudites nanoestructuradas under different manufacturing processes, in particular compounds of the type Co-Ni-Sb, conducting a study of their intrinsic characteristics related thermoelectric properties as is the figure of merit using tools designed for that purpose by making analogies with the behavior of materials classics. It also shows the development of specific instruments. Chapter 2 has been devoted to the presentation of a series of models monomódulo and the basic structure of the thermoelectric system with the aim of the behavior of different visions before pellet simulation. The model bases its continuous development in the use of media parameters taken from different conceptions depending on the temperature and on the entire semiconductor materials. With the use of models based on finite element simplifies the realization of software support because it is relatively easier to enter parameters in each of the elements which divides the material. In chapter 3 has developed the study of some compounds thermoelectric based on BiTe. There has been the characterization of a compound based on (Bi2Te3) 1-xy (Sb2Te3) x (Sb2Se3), which seeks to exploit the characteristics of BiTe at ambient temperatures (about 300K). Previously there has developed a series of theoretical concepts that explain various techniques in the development of thermoelectric materials and design in 2D quantum well that brings many benefits as they get figures of merit higher than in bulk. Finally, in Chapter 3 has been studied a monomódulo based on the materials studied. In chapter 4 has been developed material Skutterudite based on experimentation that forms the essential part of this thesis. The system Skutterudite possesses the basic conditions for obtaining a high figure of merit Z. The Skutterudites form covalent structures with low coordination between atoms that is what contributes to the possible incorporation of new atoms in the interstitial great vacuum that exists. New compounds can be formed from new atoms embedded in a vacuum interstitial which contributes to the optimization of thermal features. We have studied solutions Skutterudites based on compounds of the type CoSb3-xAsx for temperatures up to 700K. In chapter 5 has been developed in conjunction with several experiments material Skutterudite developed through nanotechnology. It is the core of this thesis is divided into three basic experiments:-Research material Co-Sb with nanoestructura. - Study material Co-Sb Nanostructured where part of the Co Neither is replaced by power plants to study their characteristics. - Study of a monomódulo formed on the basis of the materials studied. In particular material type CoSb3 (M1), which serves as the material type n Zn4Sb3 serving as the material type P. The results obtained can be the basis for the study of materials are also based on CoSb3, but with the replacement of its structure by new elements. The Nb (Niobium) is a research and acts as dopante p-type replacing Co atoms. The electrical conductivity is feasible to be increased in the compound final, although future lines of research confirm its usefulness. Another line of research that could be derived from the study in this thesis is conducting structures thermoelectric (cell power plants) based on the material studied.

Author: ZUBIAGA MONSALVE ASIER.
Year: 2006.
University: PAÍS VASCO [www.ehu.es].
Place of defense: FACULTAD DE CIENCIS Y TECNOLOGÍA.
Place of preparation: FACULTAD DE CIENCIA Y TECNOLOGÍA UPV/EHU.

Summary: For many interesting applications of technology (eg LEDs, lasers, radiation sensors, etc.) is very important to the quality of the material. This memory has been studied two compounds semiconductor major technological: ZnO and GaTe. For the characterization of them have been used, primarily, two spectroscopic techniques: fotoluminiscencia and positron annihilation. The aim has been to the analysis, identification and assignment of the existing shortcomings and to open new avenues for improving the quality of the materials and thus improved their potential applications of technological interest.