T. Mchedlidze

High-Resolution Photoinduced Transient Spectroscopy of Electrically Active Iron-Related Defects in Electron Irradiated High-Resistivity Silicon

High-resolution photoinduced transient spectroscopy (HRPITS) has been employed to investigate iron-related point defects produced by electron irradiation in high-resistivity silicon. The measurements revealed 16 traps with activation energies ranging from 14 to 530 meV. From the comparison of results, obtained by the HRPITS and ESR measurements performed on the same samples, a trap positioned at Ev+500 meV was attributed to the iron-vacancy pair (Fei)V and that positioned at EV+530 meV to the vacancy complex with two iron atoms (Fei)2V. The former is found to be stable at 400°C, while the latter anneals out at this temperature similarly to the trap at EV+410 meV related to interstitial iron. As a result of the transformation of the (Fei)2V complex and reactions of the interstitial iron with native defects, new iron-related traps with activation energies of 85, 220 and 380 meV are formed.

Properties of an Iron–Vacancy Pair in Silicon

The peculiarities of formation and annealing, and energy level position of an iron–vacancy (FeV) pair in silicon were investigated using electron-spin resonance (ESR) and photo-ESR methods. The pairs are created in iron-doped float-zone grown silicon samples during electron-irradiation and survive annealing treatment at temperatures of 400–500°C. Results of a photo-ESR study suggest that FeV in silicon is a hole trap with an energy level positioned at about 0.51 eV above the valence band. The complexes of a vacancy and two iron atoms (2FeV) are less stable than the FeV pairs and anneal out at 300–350°C in the same samples.

ESR Spectra from Platinum-Hydrogen Pair in Silicon

Parameters and some properties of two hitherto unreported platinum-related ESR spectra in silicon are reported. Spectra were detected from platinum-(Pt) and hydrogen-(H) doped silicon samples. Both spectra were analyzed with the spin state of related defect S=1/2 and revealed monoclinic (C1h) and trigonal (C3v) symmetry. The PtH and PtFe pairs in a neutral charge state are suggested to be defects responsible for the spectra.

Platinum–hydrogen complexes in silicon observed by measurements of optical absorption and electron spin resonance

Platinum–hydrogen (Pt–H) complexes in Si doped with Pt and H by heating at 1000–1300 °C followed by quenching in water were investigated from the measurements of optical absorption at 5 K and electron spin resonance (ESR) at 8 K. Optical absorption peaks at 1909.1 and 1910.3 cm−1 were observed in addition to the peaks due to the PtH and PtH2 complexes. The H doping temperature dependence of these peaks showed that the number of H atoms in the complex responsible for the 1909.1 cm−1 peak is larger than that for the 1910.3 cm−1 peak. We also observed ESR signals due to the PtH3 complex. The annealing behaviors of the 1910.3 cm−1 peak and the ESR signals were almost the same. Based on these results, the 1909.1 and 1910.3 cm−1 peaks are, respectively, assigned to the PtH4 complex and the PtH3 complex.

An iron–phosphorus pair in silicon

Fo rn -type (phosphorus-doped) floating-zone grown silicon samples, a hitherto unreported ESR signal was detected after the samples were doped with iron and irradiated with electrons. Analysis of the hyperfine structure and the angular dependence of the resonance peak positions of the spectrum, labelled TU6, indicated that the signal originates from a defect complex of monoclinic-I symmetry containing single phosphorus and single iron atoms. The spectrum can be described in terms of a paramagnetic system with S = 1/ 2a ndg values greatly deviating from that of a free electron, as well as spin S = 3/ 2a ndg ≈ 2. The spin S = 3/ 2m ay correspond to a positively charged iron atom (3d 7 state) and, thus, to a doubly positive charge state of a TU6 related complex. The fact that the TU6 signal was detected only under strong external illumination for n-type samples also supports this assignment. Results obtained during isochronal annealing of the irradiated samples suggest the possible involvement of a divacancy in the formation of an iron–phosphorus pair in silicon.

Electron spin resonance signal from a tetra-interstitial defect in silicon

The Si-B3 electron spin resonance (ESR) signal from agglomerates of self-interstitials was detected for the first time in hydrogen-doped float-zone-grown silicon samples subjected to annealing after electron irradiation. Previously this signal had been detected only in neutron- or proton-irradiated silicon samples. The absence of obscuring ESR peaks for the investigated samples at applied measurement conditions allowed an investigation of the hyperfine structure of the Si-B3 spectra. The analysis supports assignment of a tetra-interstitial defect as the origin of the signal.

Properties of Platinum–Hydrogen Complexes in Silicon: an ESR Study

For platinum (Pt) doped silicon samples co-doped with hydrogen (1H) and deuterium (2H) the principal g values of the ESR signal of the Pt2H pair were found to significantly differ from that of the Pt1H pair, signifying the presence of an isotopic shift for the g-tensor. In similar samples, energy level positions of the PtH pair and the PtH3 complex were determined from the results of photo-ESR studies. Two energy levels of the PtH pair were found to be positioned at EC-0.47 eV and EV+0.56 eV. The energy level of the PtH3 complex was found to be positioned at EC-0.73 eV.

Author's comment on “New electron spin resonance spectra from iron–vacancy pair in silicon: I. Defect with two values for the spin. II. Hyperfine interactions and isotopic effect”

Abstract We abandon our interpretation of the ESR spectra from an iron–vacancy pair in silicon. Anisotropy of peak positions and that of peak intensity of the spectra can be fitted with the spin Hamiltonian parameters for the previously reported NL19 ESR spectra. Thus, there is no necessity for the new model of the defect proposed by us in the previous publications. However, we point out several important properties of the ESR signal which led us to the erroneous interpretation.

Many optical absorption peaks observed in electron-irradiated n-type Si

The properties of many optical absorption peaks in electron-irradiated n-type Si crystals were studied. Specimens were prepared from various Si crystals. After chemical etching, they were irradiated with 3 MeV electrons at room temperature (RT). Their optical absorption spectra were measured with a Fourier transform infrared spectrometer at temperatures in the range of 7 K to RT with a resolution of 0.25 cm−1. Many optical absorption peaks were observed in the wave number range between 850 and 1600 cm−1 only in n-type (phosphorus-doped) Si crystals. Hence, they are due to donors. Such peaks were very weak in Czochralski-grown Si (Cz Si) crystals. This suggests that these peaks are due to complexes of phosphorus and vacancies since most vacancies in Cz Si form pairs (A center) with oxygen because of the very high concentration of oxygen in those crystals. They disappeared as the result of annealing at above 175 °C. Temperature dependencies of intensities of various peaks were studied.

New electron spin resonance spectra from iron–vacancy pair in silicon: II. Hyperfine interactions and isotopic effect

Abstract We studied the TU2 and TU3 ESR spectra from an iron–vacancy pair in iron-doped and electron-irradiated float-zone grown silicon samples. Isotopic shifts in the fine structure term and hyperfine and superhyperfine interaction terms of the spin Hamiltonian are considered in detail. We obtained that the change in the spin value of the defect is accompanied by a modification of the iron atom position. The existing model fails to explain observed large anisotropy of the isotopic effect.