Vacancy-oxygen defects in p-type Si1−xGex

Oxygen-vacancy defects and, in particular, the VO pairs (known as A-centers) are common defects in silicon (Si) with a deleterious impact upon its properties. Although oxygen-vacancy defects have been extensively studied in Si there is far less information about their properties in p-type doped silicon germanium (Si1−x Ge x). Here, we use Fourier transform infrared spectroscopy to determine the production and evolution of oxygen-vacancy defects in p-type Si1−x Ge x. It was determined that the increase of Ge content affects the production and the annealing behavior of the VO defect as well as its conversion to the VO2 defect. In particular, both the VO production and the VO annealing temperature are reduced with the increase of Ge. The conversion ratio [VO2]/[VO] also decreases with the increase of x, although the ratios [VO3]/[VO2] and [VO4]/[VO3] show a tendency to increase for larger Ge contents. The results are discussed in view of recent experimental and theoretical studies in Si and Si1−x Ge x. Publisher statement: Copyright 2014 AIP Publishing. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in Sgourou, E.N. , Londos, C.A. and Chroneos, A. (2014) Vacancy-oxygen defects in p-type Si1−xGex. Journal of Applied Physics, volume 116 (Article number 133502) and may be found at http://scitation.aip.org/content/aip/journal/jap/116/13/10.1063/1.489672

Infrared studies of the evolution of the CiOi(SiI) defect in irradiated Si upon isothermal anneals

Carbon-oxygen-self-interstitial complexes were investigated in silicon by means of Fourier transform infrared spectroscopy. Upon irradiation, the CiOidefect (C3) forms which for high doses attract self-interstitials (SiIs) leading to the formation of the CiOi(SiI) defect (C4) with two well-known related bands at 939.6 and 1024 cm−1. The bands are detectable in the spectra both in room temperature (RT) and liquid helium (LH) temperature. Upon annealing at 150 °C, these bands were transformed to three bands at 725, 952, and 973 cm−1, detectable only at LH temperatures. Upon annealing at 220 °C, 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 °C 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 °C 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 °C triggers the capturing of SiIs by the C4defect 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 °C, additional SiIs are captured by the CiOi(SiI)2defect leading to the formation of the CiOi(SiI)3 complex, which in turn on annealing at 280 °C converts to the CiOi(SiI)4 complex. The latter defect anneals out at 315 °C, without being accompanied in the spectra by the growth of new bands

5' Guanylylimidodiphosphate, a potent activator of adenylate cyclase systems in eukaryotic cells

5' Guanylylimidodiphosphate (Gpp(NH)p) stimulates adenylate cyclase [ATP pyrophosphate lyase (cyclizing), EC 4.6.1.1] activity in plasma membranes isolated from frog and salmon erythrocytes, from rat adrenal, hepatic, and fat cells, and from bovine thyroid cells. The nucleotide acts cooperatively with the various hormones (glucagon, secretin, ACTH, thyrotropin, and catecholamines) that stimulate these adenylate cyclase systems with resultant activities that equal or exceed those obtained with hormone plus GTP or with fluoride ion. In the absence of hormones, Gpp(NH)p is a considerably more effective activator than GTP, and, under certain conditions of incubation, stimulates rat fat cell adenylate cyclase to levels of activity (about 20 nmoles of 3',5' adenosine monophosphate mg protein per min) far higher than reported hitherto for any adenylate cyclase system examined. The nucleotide activates frog erythrocyte adenylate cyclase when the catecholamine receptor is blocked by the competitive antagonist, propranolol, and activates the enzyme from an adrenal tumor cell line which lacks functional ACTH receptors. In contrast, Gpp(NH)p does not stimulate adenylate cyclase in extracts from Escherichia coli B. Gpp(NH)p appears to be a useful probe for investigating the mechanism of hormone and nucleotide action on adenylate cyclase systems in eukaryotic cells.published_or_final_versio

Oxygen aggregation kinetics, thermal donors and carbon-oxygen defect formation in silicon containing carbon and tin

Localized vibrational mode spectroscopy measurements on Czochralski silicon (Cz-Si) samples subjected to isothermal annealing at 450 °C are reported. First, 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. Second, 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. Third, 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

Impact of isovalent doping on the formation of the CiOi(SiI)n defects in silicon

It has been determined that carbon-oxygen-self-interstitial defects in silicon (Si) can influence the operation of devices through the concentration of intrinsic point defects. Doping with larger isovalent dopants such as germanium (Ge) and tin (Sn) can impact the formation, energetics and structure of defect clusters in Si. In the present study we use density functional theory calculations to gain insights on the formation and stability of the CiOi(SiI)n (n = 0, 1, 2) defects in Si doped with Ge or Sn. It is calculated that the CiOi(SiI)n defects will preferentially form away from the oversized dopants. This result for the interstitial clusters is opposite to what is expected for vacancy-containing clusters which strongly associate with oversized dopants.Publisher Statement: NOTICE: this is the author’s version of a work that was accepted for publication in Solid State Communications. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Solid State Communications, [263, (2017)] DOI: 10.1016/j.ssc.2017.06.010© 2017, Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0

Controlling A-center concentration in silicon through isovalent doping: Mass action analysis

It has been determined experimentally that doping silicon with large isovalent dopants such as tin can limit the concentration of vacancy-oxygen defects, this in turn, can be deleterious for the materials properties and its application. These results have been supported by recent calculations based on density functional theory employing hybrid functional. In the present study, we employ mass action analysis to calculate the impact of germanium, tin and lead doping on the relative concentrations of vacancy-oxygen defects and defect clusters in silicon under equilibrium conditions. In particular, we calculate how much isovalent doping is required to constrain vacancy-oxygen concentration in silicon and conclude that Sn and Pb doping are the most effective isovalent dopants. The results are discussed in view of recent experimental and computational results

G-centers in irradiated silicon revisited: A screened hybrid density functional theory approach

Electronic structure calculations employing screened hybrid density functional theory are used to gain fundamental insight into the interaction of carbon interstitial (Ci) and substitutional (Cs) atoms forming the CiCs defect known as G-center in silicon (Si). The G-center is one of the most important radiation related defects in Czochralski grown Si. We systematically investigate the density of states and formation energy for different types of CiCs defects with respect to the Fermi energy for all possible charge states. Prevalence of the neutral state for the C-type defect is established. Publisher statement: Copyright 2014 AIP Publishing. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in Wang, H. , Chroneos, A. , Londos, C.A. , Sgourou, E.N. and Schwingenschlögl, U. (2014) G-centers in irradiated silicon revisited: A screened hybrid density functional theory approach. Journal of Applied Physics, volume 115 (Article number 183509) and may be found at http://scitation.aip.org/content/aip/journal/jap/115/18/10.1063/1.487565

Carbon related defects in irradiated silicon revisited

Electronic structure calculations employing hybrid functionals are used to gain insight into the interaction of carbon (C) atoms, oxygen (O) interstitials, and self-interstitials in silicon (Si). We calculate the formation energies of the C related defects C(i)(Si(I)), C(i)O(i), C(i)C(s), and C(i)O(i)(Si(I)) with respect to the Fermi energy for all possible charge states. The C(i)(Si(I))(2+) state dominates in almost the whole Fermi energy range. The unpaired electron in the C(i)O(i)(+) state is mainly localized on the C interstitial so that spin polarization is able to lower the total energy. The three known atomic configurations of the C(i)C(s) pair are reproduced and it is demonstrated that hybrid functionals yield an improved energetic order for both the A and B-types as compared to previous theoretical studies. Different structures of the C(i)O(i)(Si(I)) cluster result for positive charge states in dramatically distinct electronic states around the Fermi energy and formation energies

The CiCs(SiI)n defect in silicon from a density functional theory perspective

Carbon is an important defect in silicon (Si) as it can interact with intrinsic point defects and affect the operation of devices. In heavily irradiated Si containing carbon the initially produced carbon interstitial - carbon substitutional (CiCs) defect can associate with self-interstitials (SiI’s) to form, in the course of irradiation, the CiCs(SiI) defect and further to form larger complexes namely CiCs(SiI)n defects by the sequential trapping of self-interstitials defects. In the present study, we use density functional theory to clarify the structure and energetics of the CiCs(SiI)n defects. Here we report that the lowest energy CiCs(SiI) and CiCs(SiI)2 defects are strongly bound with -2.77 eV and -5.30 eV, respectively