Material characterization with terahertz time-domain spectroscopy

Köseoğlu, Devrim
Terahertz time-domain spectroscopy systems were developed and used for the anaylsis and characterization of various materials. By using ultra-fast Ti:Sapphire and Er-doped fiber lasers, terahertz time-domain spectrometers of different configurations were constructed and tested. To increase the accuracy and sensitivity of the measurements, the systems were optimized for spectroscopic analysis. MBE grown nominally undoped epitaxial GaAs samples were used for the spectroscopic measurements. These samples were first charactrized by electrical measurements in order to check the accuracy of the terahertz time-domain experiments. We have shown that the terahertz time-domin spectroscopic techniques provides a quick way of the determining the real ( ) and complex () components of the refractive index of material. In addition, we have investigated the photoexcitation dynamics of these GaAs samples. We have demonstrated that direct and photoexcited terahertz time-domain measurements give an estimate of the carrier densities and both the hole and electron mobility values with good precision. rnin An algorithm is developed to prevent the unwanted Fabry-Perot reflections which is commonly encountered in Terahertz Spectroscopy systems. We have performed terahertz time-domain transmission measurements on ZnTe <110> crystals of various thicknesses to test the applicability of this algorithm. We have shown that the algorithm developed provides a quick way of eliminating the “etalon” reflections from the data. In addition, it is also shown that these “etalon” effects can be used for the frequency calibration of terahertz time-domain spectrometers.


Applications in broadband THz spectroscopy towards material studies
Türkşen, Zeynep; Altan, Hakan; Department of Physics (2011)
The purpose of this work was to construct and analyze a THz time domain spectroscopy (THz-TDS) system by using a nanojoule energy per pulse ultrafast laser (non-amplified ultrafast laser or oscillator) source and a non-linear optical generation method for THz generation. First a THz-TDS system, which uses photoconductive antenna (PCA) method for THz generation, was built to understand the working principles of these types of systems. This THz-TDS system which used PCA for generation and a 2mm thick <110> Zn...
Si nanocrystals in sic matrix and infrared spectroscopy of in a dielecric matrix
Gencer İmer, Arife; Turan, Raşit; Department of Physics (2010)
This study focuses on various aspects of nanocrystals embedded in a dielectric matrix. In the first part of this work, a new approach with the use of Fourier Transform Infrared spectroscopy (FTIR) in the nanocrystal analysis was developed and presented. Si and Ge nanocrystals embedded in SiO2 matrix were mainly studied. This new approach is based on the analysis of structural variations of SiO2 matrix during the formation of semiconductor nanocrystlas. It is shown that the chemical and structural variations...
Space-charge-limited currents and photoconductive properties of Tl2InGaSe4 layered crystals
QASRAWI, ATEF FAYEZ HASAN; Hasanlı, Nızamı (Informa UK Limited, 2008-01-01)
The extrinsic electronic parameters of Tl2InGaSe4 layered crystals were investigated through measurement of the temperature-dependent dark conductivity, space-charge-limited currents and photoconductivity. Analysis of the dark conductivity reveals the existence of two extrinsic energy levels at 0.40 and 0.51 eV below the conduction band edge, which are dominant above and below 260 K, respectively. Current-voltage characteristics show that the one at 0.51 eV is a trapping energy level with a concentration of...
Optical properties of silicon based amorphous thin films
Akaoğlu, Barış; Katırcıoğlu, Bayram; Department of Physics (2004)
Silicon based hydrogenated amorphous semiconducting (intrinsic and n/p doped a-Si:H and a-Si1-xCx:H) thin films have been deposited by plasma enhanced chemical vapor deposition (PECVD) system. In order to analyze the optical response of these amorphous films, intrinsic optical absorption mechanisms have resumed and spectral variations of absorption coefficient ?(E) are derived. The exponential variation of absorption coefficient for energies below the band edge is discussed in the frame of randomly distribu...
Transport studies of carbon-rich a-SiCx : H film through admittance and deep-level transient spectroscopy measurements
Atilgan, I; Ozdemir, O; Akaoglu, B; Sel, K; Katircioglu, B (Informa UK Limited, 2006-07-01)
An intrinsic, carbon- rich a- SiCx: H thin film, prepared by the plasma- enhanced chemical vapour deposition ( PECVD) technique, has been studied mainly by AC admittance and small- pulse deep- level transient spectroscopy ( DLTS) measurements on an Al/ a- SiCx: H/ p- Si metal - insulator - semiconductor ( MIS) structure. The effects of measurement temperature, voltage and small- signal AC modulation frequency on the MIS capacitor are qualitatively and quantitatively described. The kinetics of charge injecti...
Citation Formats
D. Köseoğlu, “Material characterization with terahertz time-domain spectroscopy,” Ph.D. - Doctoral Program, Middle East Technical University, 2010.