Unit:
Department of PhysicsLibrary of the School of Science
Author:
Angeletos Theocharis
Dissertation committee:
Λυκοδήμος Βλάσιος, Αναπληρωτής Καθηγητής, Τμήμα Φυσικής, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών.
Ράπτης Ιωάννης, Καθηγητής, Σχολή Εφαρμοσμένων Μαθηματικών και Φυσικών Επιστημών, Εθνικό Μετσόβιο Πολυτεχνείο.
Γαρδέλης Σπυρίδων, Αναπληρωτής Καθηγητής, Τμήμα Φυσικής, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών.
Παπαθανασίου Αντώνιος, Επίκουρος Καθηγητής, Τμήμα Φυσικής, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών.
Σιμσερίδης Κωνσταντίνος, Αναπληρωτής Καθηγητής, Τμήμα Φυσικής, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών.
Σκορδάς Ευθύμιος, Αναπληρωτής Καθηγητής, Τμήμα Φυσικής, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών.
Σταμόπουλος Δημοσθένης, Αναπληρωτής Καθηγητής, Τμήμα Φυσικής, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών.
Original Title:
Μελέτη ατελειών στο πυρίτιο με τη χρήση υπέρυθρης φασματοσκοπίας
Translated title:
Studies of crystal defects in silicon by means of IR spectroscopy
Summary:
In the first experimental work (Ch.3) we have reported infrared spectroscopy studies in neutron irradiated Cz-Si containing carbon. The material was thermally treated at high temperature prior to irradiation. The aim was to investigate the production and annealing of the CiOi(SiI) defect well-known as C4 center. Besides the two standard LVMs at 934 and 1018 cm-1 detected always in room temperature measurements another band was also detected at 760 cm-1. The latter band has the same annealing behavior as the 934 and 1018 cm-1 bands. Its existence has been predicted by theoretical calculations previously, but it has not reported definitely so far experimentally. The present study verifies unambiguously its presence. Upon annealing the above three bands begin to decay in the spectra at ~ 140 Co and disappear at ~200 Co. No other bands appear to arise in the spectra upon the disappearance of the above bands. Semi-empirical calculations of the LVMs frequencies of the C4 complex verify the correlation of the 760 cm-1 band with this center. The annealing kinetics of the bands was investigated and it was found that their decay follows a second order reaction with an average activation energy of E ~ 0.50 ±0.02 eV.
In the second experimental work (Ch.4) carbon-oxygen-self-interstitial complexes were investigated in silicon by means of Fourier Transform Infrared Spectroscopy (FTIR). Upon irradiation, the CiOi defect (C3) forms, which for high doses attracts self-interstitials (SiI’s) leading to the formation of the CiOi(SiI) defect (C4) with two well-known related bands at 939.6 and 1024 cm-1 at LH. The bands are detectable in the spectra both at RT and LH. Upon annealing at 150 oC, these bands were transformed to three bands at 725, 952 and 973 cm-1, detectable only at LH temperatures. Upon annealing at 220 oC, these bands were transformed to three bands at 951, 969.5 and 977 cm-1, detectable both at RT and LH temperatures. Annealing at 280 oC, resulted in the transformation of these bands to two new bands at 973 and 1024 cm-1. The latter bands disappear from the spectra upon annealing at 315 oC without the emergence of other bands in the spectra. Considering reaction kinetics and defect metastability we developed a model to describe the experimental results. Annealing at 150 oC triggers the capturing of SiI’s by the C4 defect leading to the formation of the CiOi(SiI)2 complex. The latter structure appears to be bistable: measuring at LH the defect is in configuration CiOi(SiI)2 giving rise to the bands at 725, 952 and 973 cm-1, whereas on measurements at RT the defect converts to another configuration CiOi(SiI)2* without detectable bands in the spectra. Possible structures of the two CiOi(SiI)2 configurations are considered and discussed. Upon annealing at 220 oC additional SiI’s are captured by the CiOi(SiI)2 defect leading to the formation of the CiOi(SiI)3 complex (~951, ~969,5 and ~977 cm-1), which in turn on annealing at 280 oC converts to the CiOi(SiI)4 complex (~973, ~1024 cm-1). The latter defect anneals out at 315oC, without being accompanied in the spectra by the growth of new bands.
In the third experimental work (Ch.5) localized vibrational mode (LVM) spectroscopy measurements on Czochralski silicon (Cz-Si) samples subjected to isothermal annealing at 450 oC are reported. Firstly, we studied the effect of carbon (C) and tin (Sn) isovalent dopants on the aggregation kinetics of oxygen. It is determined that the reduction rate of oxygen is described by the Johnson-Mehl-Avrami equation in accordance with previous reports. The activation energy related with the reaction rate constant of the process is calculated to increase from Cz-Si, to C-doped Cz-Si (CCz-Si), to Sn-doped Cz-Si contained C (SnCz-Si). This is attributed to the presence of the isovalent dopants that may impact both the kinetics of the oxygen atoms and also may lead to the formation of other oxygen- related clusters. Secondly, we studied the effect of Sn on the formation and evolution of carbon-oxygen (C-O) defects. It was determined that the presence of Sn suppresses the formation of the C-O defects as indicated by the reduction in the strength of the 683, 626 and 586 cm-1 well-known bands of CsOi defect. The phenomenon is attributed to the association of Sn with C atoms that may prevent the pairing of O with C. Thirdly, we investigated the effect of C and Sn on the formation of thermal donors (TDs). Regarding carbon our results verified previous reports that carbon suppresses the formation of TDs. Interestingly, when both C and Sn are present in Si , very weak bands of TDs were observed, although it is known that Sn alone suppress their formation. This may be attributed to the competing strains of C and Sn in the Si lattice.
In the fourth experimental work (Ch.6) we employ Fourier Transform Infrared Spectroscopy (FTIR) to study the evolution of O and C concentration as well as the evolution of the oxygen precipitate bands in electron- irradiated Sn-doped Si, subjected to isochronal anneals up to 950 oC. Special attention was given in connecting infrared absorption bands with certain precipitation morphologies. In this study, bands at 1040, 1060, 1080 and 1170 cm-1 generally attributed to precipitate morphologies were detected. Using arguments from classical theoretical mechanics we have attributed the 1040 cm-1 band to a structure more close to a spherical morphology, although the 1060 and 1080 cm-1 bands were attributed to structures more close to octahedral and polyhedral morphologies, respectively. Additionally the band at 1170 cm-1 was attributed to platelet precipitates. The effect of C and (C, Sn) co-doping Si in the morphologies of the precipitates bands was investigated in detail. It was found that in the irradiated material C suppresses the formation of spheroidal precipitates although it enhances the platelet precipitates, whereas in Si containing C and Sn the opposite behavior was detected. The presence of the two impurities modifies the number of the O precipitates and affects the relative density among the formed morphologies in Si, determining whether the spheroidal or platelet precipitates will prevail. The phenomenon was discussed taking into consideration the effect of the density of the nucleation sites on the interfacial energy of the precipitates. Furthermore, an inverse annealing stage in the evolution curve of C, namely an increase of C concentration prior to its complete disappearance was studied. This recovery stage was determined to be enhanced in (C, Sn) co-doping Si with relatively low Sn content, although in Si with high Sn content the increase of C is substantially lower. An explanation was suggested based on the ability of the Sn to temporarily trap vacancies, thus affecting the restoration of the C substitutional atoms in the Si lattice.
Main subject category:
Science
Keywords:
Infrared spectroscopy (FTIR), Optical properties, Semiconductors – Silicon, Crystalline defects, Carbon, Oxygen, Isovalent impurities, Dopping, Termal treatments, Annealing, Neutron/electron irradiation, Thermal donors, Precipitates, Czochralski method.
Number of references:
380
