Photoluminescence specroscopy of CdS and GaSe

Seyhan, Ayşe
With the use of photoluminescence (PL) spectroscopy one can able to get a great deal of information about electronic structure and optical processes in semiconductors by the aid of optical characterization. Among various compound semiconductors, Cadmium Sulfide (CdS) and Gallium Selenide (GaSe) are interesting materials for their PL emissions. Particularly, due to its strong anisotropy, investigation of GaSe necessitates new experimental approaches to the PL technique. We have designed, fabricated and used new experimental set-up for this purpose. In this thesis, we have investigated the PL spectra of both CdS and GaSe as a function of temperature. We observed interesting features in these samples. These features were analyzed experimentally and described by taking the band structure of the crystals into account. From the excitonic emissions, we determined the bandgap energy of both materials. We studied various peaks that appear in the PL spectra and their origin in the material. We have found that donor acceptor transitions are effective in CdS at low temperatures. A transition giving rise to a red emission was observed and attributed to a donor level which is likely to result form an S vacancy in CdS crystal. The PL peaks with energy close to the bandgap were observed in GaSe. These peak were attributed to the bound excitons connected either to the direct or indirect band edge of GaSe. The striking experimental finding in this work was the PL spectra of GaSe measured in different angular position with respect to the crystal axis. We observed that PL spectra exhibit substantial differences when the angular position of the laser beam and the detector is changed. The optical anisotropy which is responsible for these differences was measured experimentally and discussed by considering the selection rules of the band states of GaSe.


Intrinsic photoconductivity of P3HT films measured by time-resolved THz spectroscopy
Esentürk, Okan; Heilweil, Edwin J. (2007-12-01)
Intrinsic photoconductivities of P3HT polymers were measured and compared by using optical pump-THz probe spectroscopy. The charge carrier mobility shows a clear dependence on the molecular weight and dispersion index of the polymers.
Vibration analysis of cracked beams on elastic foundation using Timoshenko beam theory
Batıhan, Ali Çağrı; Kadıoğlu, Fevzi Suat; Department of Mechanical Engineering (2011)
In this thesis, transverse vibration of a cracked beam on an elastic foundation and the effect of crack and foundation parameters on transverse vibration natural frequencies are studied. Analytical formulations are derived for a beam with rectangular cross section. The crack is an open type edge crack placed in the medium of the beam and it is uniform along the width of the beam. The cracked beam rests on an elastic foundation. The beam is modeled by two different beam theories, which are Euler-Bernoulli be...
KIRAGI, H; Ersak, Aydın (1994-04-14)
In this paper an object recognition and localization system based on ultrasonic range imaging to be used in optically opaque environments is introduced. The system is especially designed for robotics applications. The ultrasonic image is acquired by scanning ultrasonic transducers in two dimensions above the area where objects are located. The features that are used for recognition and localization processes are extracted from the outermost boundaries of the objects present in the input scene. Experimental ...
Spectroscopic ellipsometry study of Si nanocrystals embedded in a SiOx matrix: Modeling and optical characterization
Ilday, Serim; Nogay, Gizem; Turan, Raşit (2014-11-01)
In this work, we report on a spectroscopic ellipsometry study of thin films of silicon nanocrystals embedded in a SiOx matrix that is performed to better understand how substoichiometric SiOx species affect the optical properties of these systems. The silicon nanocrystals are fabricated in a SiOx matrix by thermal annealing of magnetron-sputtered thin films in a wide range of x values (0< x< 2) in order to produce every possible substoichiometric SiOx species in various fractions. A generic optical model to...
Optical characterization of CuIn5S8 crystals by ellipsometry measurements
IŞIK, MEHMET; Gasanly, Nizami (2016-04-01)
Optical properties of CuIn5S8 crystals grown by Bridgman method were investigated by ellipsometry measurements. Spectral dependence of optical parameters; real and imaginary parts of the pseudodielectric function, pseudorefractive index, pseudoextinction coefficient, reflectivity and absorption coefficients were obtained from the analysis of ellipsometry experiments performed in the 1.2-6.2 eV spectral region. Analysis of spectral dependence of the absorption coefficient revealed the existence of direct ban...
Citation Formats
A. Seyhan, “Photoluminescence specroscopy of CdS and GaSe,” M.S. - Master of Science, Middle East Technical University, 2003.