Optical Properties of Sb2Te3, and Dilute Magnetic Semiconductors Sb1.97 VO.03 Te3 and Sb1.94 CrO.06 Te3

This thesis reports on the optical properties of the dilute magnetic semiconductors, Sb1.97 V 0.03 Te3 and Sb1.94Cr0.06Te3, along with the parent compound Sb2Te3' These materials develop a ferromagnetic state at low temperature with Curie temperatures of 22 K and 16 K respectively. All three samples were oriented such that the electric field vector of the light was perpendicular to the c-axis. The reflectance profile of these samples in the mid-infrared (500 to 3000 cm-1) shows a pronounced plasma edge which retracts with decreasing temperature. The far-infrared region of these samples exhibits a phonon at ~ 60 cm-1 which softens as temperature decreases. Kramers-Kronig analysis and a Drude-Lorentz model were employed to determine the optical constants of the bulk samples. The real part of the optical conductivity is shown to consist of intraband contributions at frequencies below the energy gap (~0.26 eV) and interband contributions at frequencies above the energy gap. The temperature dependence of the scattering rate show that a mix of phonon and impurity scattering are present, while the signature of traditional spin disorder (magnetic) scattering was difficult to confirm.

Optical absorption studies in ion implanted and amorphous semiconductors - Investigations in some tetrahedrally co-ordinated and chalcogenide materials

The thesis provides an overall review and introduction to amorphous semiconductors, followed by a brief discussion on the important structural models proposed for chalcogenide glasses and their electrical, optional and thermal properties. It also gives a brief description of the Physics of thin films, ion implantation and Photothermal Deflection Spectroscopy. A brief description of the experimental setup of a photothermal deflection spectrometer and the details of the preparation and optical characterization of the thin film samples. It deals with the employment of the subgap optional absorption measurement by PDS to characterize the defects, amorphization and annealing behavior in silicon implanted with B+ ions and the profiles of ion range and vacancy distribution obtained by the TRIM simulation. It reports the results of all absorption measurements by PDS in nitrogen implanted thin film samples of Ge-Se and As-Se systems

Growth and characterization of nanostructured wide band gap semiconductors for optoelectronic applications

Department of Physics, Cochin University of Science and Technology

Synthesis and Characterization of Some Organic Semiconductors and Investigations on the Effect of Swift Heavy Ions on Their Properties

In this work polymers belonging to polyaniline and polyaniline doped with camphor sulphonic acid are synthesised. Cobalt phthalocyanine is an interesting candidate belonging to the tetramers. Studies on the composites containing cobalt phthalocyanine tetramer and polyaniline doped with camphor sulphonic acid for various concentration are also undertaken in order to understand the mechanism. RF plasma polymerised aniline and furfural are prepared. The structural and electrical properties are evaluated. The bombardment of swift heavy ions of these films are carried out and the effect of irradiation on their properties is also investigated.

Comment on "Reappraisal of experimental values of third-order elastic constants of some cubic semiconductors and metals"

In a recent paper A. S. Johal and D. J. Dunstan [Phys. Rev. B 73, 024106 (2006)] have applied multivariate linear regression analysis to the published data of the change in ultrasonic velocity with applied stress. The aim is to obtain the best estimates for the third-order elastic constants in cubic materials. From such an analysis they conclude that uniaxial stress data on metals turns out to be nearly useless by itself. The purpose of this comment is to point out that by a proper analysis of uniaxial stress data it is possible to obtain reliable values of third-order elastic constants in cubic metals and alloys. Cu-based shape memory alloys are used as an illustrative example.

Photoacoustic investigation of the optical and thermal properties of selected amorphous chalcogenide semiconductors

This thesis work has mainly concentrated on the investigation of the ,optical and thermal properties of binary semiconducting chalcogenide glasses belonging to the AivB¥5x and AZBXEX families. The technique used for these studies is a relatively new one namely, the photoacoustic (PA) technique. This technique is based on the detection of acoustic signal produced in an enclosed volume when the sample is irradiated by an intensity modulated radiation. The signal produced depends upon the optical properties of the sample, and the thermal properties of the sample, backing material and the surrounding gas. For the present studies an efficient signal beam gas-microphone PA spectrometer, consisting of a high power Xenon lamp, monochromator, light beam chopper, PA cell with microphone and lock-in amplifier, has been set up. Two PA cells have been fabricated: one for room temperature measurements and another for measurements at high temperatures. With the high temperature PA cell measurements can be taken upto 250°C. Provisions are incorporated. in both the cells to change the volume and to use different backing materials for the sample. The cells have been calibrated by measuring the frequency response of the cells using carbon black as the sample

High Indium Concentration InGaN/GaN Grown on Sapphire Substrate by MOCVD

The InGaN system provides the opportunity to fabricate light emitting devices over the whole visible and ultraviolet spectrum due to band-gap energies E[subscript g] varying between 3.42 eV for GaN and 1.89 eV for InN. However, high In content in InGaN layers will result in a significant degradation of the crystalline quality of the epitaxial layers. In addition, unlike other III-V compound semiconductors, the ratio of gallium to indium incorporated in InGaN is in general not a simple function of the metal atomic flux ratio, f[subscript Ga]/f[subscript In]. Instead, In incorporation is complicated by the tendency of gallium to incorporate preferentially and excess In to form metallic droplets on the growth surface. This phenomenon can definitely affect the In distribution in the InGaN system. Scanning electron microscopy, room temperature photoluminescence, and X-ray diffraction techniques have been used to characterize InGaN layer grown on InN and InGaN buffers. The growth was done on c-plane sapphire by MOCVD. Results showed that green emission was obtained which indicates a relatively high In incorporation.

High Optical Quality Nanoporous GaN Prepared by Photoelectrochemical Etching

Nanoporous GaN films are prepared by UV assisted electrochemical etching using HF solution as an electrolyte. To assess the optical quality and morphology of these nanoporous films, micro-photoluminescence (PL), micro-Raman scattering, scanning electron microscopy (SEM), and atomic force microscopy (AFM) techniques have been employed. SEM and AFM measurements revealed an average pore size of about 85-90 nm with a transverse dimension of 70-75 nm. As compared to the as-grown GaN film, the porous layer exhibits a substantial photoluminescence intensity enhancement with a partial relaxation of compressive stress. Such a stress relaxation is further confirmed by the red shifted E₂(TO) phonon peak in the Raman spectrum of porous GaN.

Atomic diffusion induced by stress relaxation in InGaAs/GaAs epitaxial layers

The origin of the microscopic inhomogeneities in InxGa1-xAs layers grown on GaAs by molecular beam epitaxy is analyzed through the optical absorption spectra near the band gap. It is seen that, for relaxed thick layers of about 2.8μm, composition inhomogeneities are responsible for the band edge smoothing into the whole compositional range (0.05

Potassium nickel(II) gallium phosphate hydrate, K[NiGa2(PO4)(3)(H2O)(2)]

The title compound, potassium nickel(II) digallium tris-( phosphate) dihydrate, K[NiGa2(PO4)(3)(H2O)(2)], was synthesized hydrothermally. The structure is constructed from distorted trans-NiO4(H2O)2 octahedra linked through vertices and edges to GaO5 trigonal bipyramids and PO4 tetrahedra, forming a three-dimensional framework of formula [NiGa2(PO4)(3)(H2O)(2)](-). The K, Ni and one P atom lie on special positions (Wyckoff position 4e, site symmetry 2). There are two sets of channels within the framework, one running parallel to the [10 (1) over bar] direction and the other parallel to [001]. These intersect, forming a three-dimensional pore network in which the water molecules coordinated to the Ni atoms and the K+ ions required to charge balance the framework reside. The K+ ions lie in a highly distorted environment surrounded by ten O atoms, six of which are closer than 3.1 angstrom. The coordinated water molecules are within hydrogen-bonding distance to O atoms of bridging Ga-O-P groups.

Gallium-sulphide supertetrahedral clusters as building blocks of covalent organic-inorganic networks

The synthesis and characterisation of novel covalent organic-inorganic architectures containing organically-functionalised supertetrahedra is described. The structures of these unique materials consist of one-dimensional zigzag chains or of honeycomb-type layers, in which gallium-sulfide supertetrahedral clusters and dipyridyl ligands alternate.

Arrays of chiral nanotubes and a layered coordination polymer containing gallium-sulfide supertetrahedral clusters

We report here a unique chiral hybrid gallium sulfide, [NC2H8]2[Ga10S16(N2C12H12)(NC2H7)2] 1, consisting of helical chains of organically-functionalised supertetrahedral clusters which form quadruple-stranded helical nanotubes of ca. 3 nm diameter. This material therefore consists of discrete metal-organic nanotubes which, to the best of our knowledge, are extremely rare. Whilst solvothermal reactions involving 1,2-di(4-pyridyl)ethylene (DPE) resulted in the formation of such single-walled chiral nanotubes, the use of longer 4,4’-trimethylenedipyridine (TMP) ligands resulted in the synthesis of a two-dimensional hybrid gallium sulfide, [C5H6N]3[Ga10S16(OH)(N2C13H14)] 2 in which, for the first time, inorganic and organic linkages between supertetrahedral clusters coexist.