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Archived Theses
Properties of electrodeposited metalic systems(Schottky diodes) on semiconductor substrates
In this study, by using n-type Si substrate with (100) orientation, 150 nm thickness and 10-20 ?m resistivity and chromium doped, thin film Schottky diode system (Cr/n-Si SBHs which is electrochemically formed on n-type Si) is constructed and characterized.In the electrical characterization of this diodes, the current ?voltoge (I-V) and the capacitance ? voltage (C-V) measurements are done.The basic diode parameters such as ideality factor (n) and barrier height (?b) were consequently extracted from electrical measurements. It has been shown that the ideality factors increased and barrier heights decreased with the decreasing temperatures, on the basis of the thermionic emission (TE) theory.The homogeneity or the uniformity of the Schottky BH is an issue with important implications on the theory of Schottky barrier formation and important ramifications for the operation of Schottky barrier diodes and contacts. Thus, provided semiconductor substrate is well characterized, the homogeneous Schottky BH may be obtained even from the I-V characteristics of one contact. For this purpose ,Cr/n-type Si SBHs with a doping density of about 1.25x1015 cm-3 is prepared and the linear region with large BHs is used. The electrical characterisitics of Cr/n-type structures were investigated in the wide temperature range (80-320 K) by steps of 20 K.Key words: Silicon, Schottky barrier diodes, Electrodeposition Method.
SnS ve SnSe?nin optik özellikleri
ABSTRACT OPTICAL PROPERTIES OF SnS and SnSe GÖNÜL (ARPA) Beşire M.S. in Engineering of Physics Supervisor: Assoc. Prof. Dr. İ.Engin TÜRE February 1991, 46 pages The optical transmission in the layered semiconductors of SnS and SnSe has been studied in the wavelength range of 200-1100 nm for the polarised light of £||a and E lib, where a and b are the crystallographic axes within the cleavage plane. Indirect bandgaps of 1.24 and 1.17 eV for SnS and 0.74 and 0.8 eV for SnSe have been found for the two directions of the polarisations Ella and Glib respectively. In the layered compound of SnSe, two indirect transitions (E... and E±2) were ] Identified as* E^l.14 ± 0.01 eV and E±2 = 1.26±0;01 eV for £ lla polarisation and E±1 = 1.12 + 0.01 eV and E±2 = 1.22 ± 0.01 eV for 6 lib polarisation. It was found that the phonon assisted transitions in SnS required the participation of two phonons with energies of 0.03 eV and 0.075 eV for Ella polarisation and 0.05 eV and 0.15 for £|fb polarisation. The K < K, relation was found to be valid in SnSe whereas K > K, a b a b relation in SnS for the whole range of energies of incident light. The compounds of SnS and SnSe were found to be strongly anisotropic from the optical measurements of these compounds. Keywords: Layered semiconductors, cleavage plane, optical transmission, absorption coefficient. iii
Thermal and optical characteristics of radiation induced defect centers in alkali Halide crystals (TLD-100)
Abstract Thermal and Optical Characteristics of Radiation Induced Defect Centers in Alkali Halide Crystals (TLD-100) " YAZICI Ahmet Necmeddin Ph.D. in P.E., University of Gaziantep Supervisor: Asst.Prof.Dr. Zihni öztürk October 1996, 168 Pages The exact cause of sensitivity loss in TLD LiF:Mg,Ti has not been completely understood yet. If a used TLD is not annealed at an elevated temperature prior to reuse, residual deep defect centers still present in dosimeter. These centers will interact with new incoming radiations and produce further centers. This will introduce significant errors in low dose measurements. If the structure, thermal and optical characteristics of these defects were better understood, then a better model could be proposed to overcome sensitivity loss. Therefore, the samples were, firstly, irradiated by p-rays to produce sufficient concentration of defect centers, then optical absorption, phototransferred thermoluminescence, and thermoluminescence measurements were made to identify defect structures in LiF:Mg,Ti with appropriate heat treatments. The changes in the optical absorption band and mglow peak areas were determined as a function of various heat treatments using a computerised deconvolution program. The similarities in the variation of curves of glow peak 5 and OA band at 310 nm suggest that they may be belong to the same traps, namely Mg-trimer/Ti complex. The lack of correspondence between peak 2 and 380 nm band indicates that peak 2 is not related to Mg-dipoles as previously suggested, but related to Ti-related/F- center complex. Deconvolution analysis of OA and glow curves produced by annealing at and above 125 °C for long times before irradiation permits the identification of a new peak at 1 75 °C and OA band at 282 nm. Due to their similar thermal decaying properties, it is thought that they may be belong to the Z2-type centers. The effects of pre-irradiation annealing on the values of trapping parameters of LiF:Mg,Ti were determined as a function of durations at 125 °C by computerized glow curve analysis. The application of pre-annealing with different durations made significant changes on the activation energies of peaks 1 to 5, especially of peak 4. These variations are due to the interactions of defects with each other during heat treatments. A new simple model was developed to describe TL emission bands of luminescent centers in solids. TL emission spectra measurements of LiF:Mg.Ti showed one main emission band at 420 nm. The individual emission bands were separated using the developed model to investigate the success of the developed model. According to this model, the emission spectrum of whole glow peaks can be successfully fitted with two emission bands. Keywords: Alkali halide, LiF:Mg,Ti, thermoluminescence, optical absorbance, emission spectra, trapping parameters. IV
Calculation of alpha half-lives of radiosotopes by using different techniques
AbstractCalculation of Alpha Half-Lives of Radioisotopes byUsingDi¤erent TechniquesSÜR, SerapM. Sc in Engineering PhysicsSupervisor: Prof. Dr. Zihni ÖZTÜRKJuly 2005The estimations and comparisions of alpha half-lives of alphaemitting isotopes of odd-odd, even-even, odd-even and even-odd nu-clei are made by using di¤erent methods. Tunnelling probabilitiesare determined by the breaking the Coulomb barrier into segments.The obtained succesive tunnelling probabilities are multiplied toobtain tunnelling probability utilized to determine alpha half-lives.The advantages and disadvantages of the model are discussed. Itis observed that an application of the simple model based on thetunnelling probability provides quite satisfactory results comparedto some other techniques.Key words: Alpha Decay, Tunnelling Probability, Half-life.1
A Monte Carlo study of long-lived particles (Neutralinos) in CMS at LHC
In this study after giving a summary of Standard Model (SM) which isthe best theory to explain the fundamental particles and the interactions betweenthem upto now, the Minimal Supersymmetric Standard Model (MSSM),a preferred extension of SM was given in detailed. The simulation of neutralinoswhich are considered to be one of the particles of structure of the dark matter andcould not be explained by SM, creates the objective of this thesis. Simulationshave been performed for a center of mass energy ps= 10 TeV and neutralinomass M0 = 165 GeV. One hundred events have been generated using the MonteCarlo simulation method. A pair of neutralinos were produced and each of themwas decayed into two jets. Two parameters have been used to investigate neutrolinosignatures. One of parameters was muon decay vertex coming from decayprocess in four jets up to 3 cm in the inner tracker. Reconstructed muon datahave been checked for all directions, then demonstrated in these directions. Theother parameter was missing transverse energy coming from jets transversingCalorimeter. The related graphs have been plotted for these particles.
The effect of various experimental parameters on glow peaks and TL kinetics of some dosimetric materials
Either natural fluride which contains, depending on its origin, a wide variety of different impurities acting as activators, or synthetic CaF2 as a host lattice with artificial dopants such as Tm, Dy, and Mn have been used as dosimeter. The samples used in this study were CaF2:Dy (TLD-200), CaF2:Tm (TLD-300) and CaF2:Mn (TLD- 400) crystal chips obtained from Harshaw Chemical Company, Ohio, USA. In this study we have investigated the effect of heating rate on the dose response and linearities of these samples by evaluating their supra / super linearity indexes, f(D) and g(D) respectively. Also the fading characteristics of the samples both in the dark and under tungsten filament lamp and the effect of heating rate on shape of the glow curves and total peak areas of the glow curves have been investigated in detail.Lithium triborate, (LiB3O5, LBO), is one of the most known lithium borates. It is a newly developed nonlinear optical crystal. In this work, the trapping parameters of Al- doped LiB3O5, synthesized in Middle East Technical University, were evaluated by using different experimental methods, namely; the additive dose repeated initial rise, variable heating rate, peak shape, isothermal decay, three points methods and the computerized glow curve deconvolution method.
Theoretical investigation of the effect of nitrogen on optical and electronic properties of GaInAsN semiconductors
The investigation of profound of nitrogen containing III-V semiconductors in fundamental properties proven experimentally and device applications and to propose new device materials are the aim of this thesis. We have presented an overview of the fundamental properties of nitrogen incorporated GaInAs semiconductor and the physics behind of unusual characteristics of GaInAsN. We have compared the band alignments of the nitrogen-free and nitrogen-included laser devices on GaAs and InP substrates. We have presented the calculations to investigate the role of N and Sb on the critical thickness hc of strained GaInAsNSb QWs on GaAs and InP substrate for (001) and (111) orientations.We have presented a new analytical method to investigate the effect of nitrogen on intrinsic carrier density, screening parameter, effective Bohr radius and binding energy of shallow donors in GaAsN alloys. We have investigated the relation between the binding energy of hydrogenic shallow donor in bulk GaAsN alloys for different screening parameter and nitrogen concentrations. We have investigated the refractive indices and the corresponding optical confinement factors of the proposed GaInAsN laser material systems on GaAs substrate. We have compared conventional and N-based quantum well laser systems to find which has better optical confinement.