Browsing by Author "Ferekides, Chris"

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The copper influence on the PL spectra of CdTe thin film as a component of the CdS/CdTe heterojunction [Articol]
(Elsevier, 2009) Vatavu, Sergiu; Zhao, Hehong; Caraman, Iuliana; Gașin, Petru; Ferekides, Chris
The influence of annealing in the presence of CdCl2 and a thin copper layer deposited onto CdTe on the photoluminescence spectra of CdTe, as a component of CdS/CdTe heterojunction, has been studied for two excitation wavelengths: 0.337 μm and 0.6328 μm. The behavior of the PL was studied as a function of the measurement temperature and excitation intensity. At 0.6328 μm excitation, the interface PL consists of a known 1.43X band, and the chloride annealing enhances radiative transitions at 1.536 eV. The intensity of the 1.536 eV transitions increases when Cu is present. The PL of as-deposited CdTe films prepared in the presence of oxygen has the 1.45X band attenuated when excited with 0.337 μm excitation wavelength.
The investigation of TCO/CdS/CdTe heterojunctions by C-U and C-f measurements: Experiment and modeling [Articol]
(IEEE, 2013) Rotaru, Corneliu; Vatavu, Sergiu; Fedorov, Vladimir; Gașin, Petru; Lux-Steiner, Martha; Ferekides, Chris; Rusu, Marin
The paper presents the analysis of C-U and C-f data obtained in the 1 kHz-10 MHz range for CdS/CdTe heterojunctions prepared by CSS onto (ZnO:Al, ZnO:Al/i-ZnO)/Glass substrates. An attempt to model the physical properties of the heterojunctions is made. A small signal analysis has been carried out to establish the equivalent circuit of device. The unusual capacitance behavior of the ZnO based heterojunction is attributed to presence of the barrier at the back contact.
Photoluminescence studies of the interface of CdS/CdTe heterojunctions [Articol]
(2009) Vatavu, Sergiu; Zhao, Hehong; Caraman, Iuliana; Gașin, Petru; Morel, Don; Ferekides, Chris
The photoluminescence analysis of CdS/CdTe interface layer of CdS/CdTe heterojunction has been carried out in the 15- 100 K temperature range. An attempt to correlate observed PL features with the CdSxTe1–x layer presence at the interface of the heterojunctions was made. It is assumed the 1.525 eV band has an excitonic origin and 1.37X PL band is a characteristic impurity band due to CdSTe layer. Comparative plots showing SnO2/CdTe PL spectra are given as well.
Photoluminesence studies of CdTe/SnO2 and CdTe/CdS heterojunctions: The influence of oxygen and the CdCl2 heat treatment [Articol]
(Elsevier, 2011) Vatavu, Sergiu; Zhao, Hehong; Caraman, Iuliana; Gasin, Petru; Ferekides, Chris
The influence of oxygen and annealing in the presence of CdCl2 on the photoluminescence (PL) spectra of CdTe, component of SnO2/CdTe heterojunction (HJ), has been studied in a temperature range of 17–100 K. The changes in the photoluminescence spectra were studied as a function of excitation intensity. Analysis of the PL spectra was carried out with considerations of spectra obtained from CdS/CdTe heterojunctions. CdTe side PL (SnO2/CdTe HJ) consisted of 1.450 eV-DA defect band and 1.243 eV band (17 K). Annealing resulted in the disappearance of 1.243 eV band in oxygen containing samples. Interface PL for the unannealed samples consisted of mainly the 1.264 eV and a trace of the defect band. The CdCl2 treatment is responsible for an almost symmetrical 1.416 eV band.
Radiative recombination mechanisms in CdTe thin films deposited by elemental vapor transport [Articol]
(Elsevier, 2015) Collins, Shamara; Vatavu, Sergiu; Evani, Vamsi; Khan, Md; Bakhsh, Sara; Palekis, Vasilios; Rotaru, Corneliu; Ferekides, Chris
A photoluminesence (PL) study of the radiative recombination mechanisms for CdTe films deposited under different Cd and Te overpressure by elemental vapor transport is presented. The experiment and analysis have been carried out in the temperature range of 12–130 K. The intensity of the PL laser excitation beam was varied by two orders of magnitude. It has been established that the bands in the 1.47–1.50 eV are determined by transitions involving shallow D and A states and the 1.36x–1.37x eV band is due to band to level transitions. Deep transitions at 1.042 eV and 1.129 eV are due to radiative transitions to levels determined by CdTe native defects.