S. B. Lastovskii

Tin-vacancy complex in germanium

Electrically active defects introduced into Ge crystals co-doped with tin and phosphorus atoms by irradiation with 6 MeV electrons have been studied by means of transient capacitance techniques and ab-initio density functional modeling. It is shown that Sn atoms are effective traps for vacancies (V) in the irradiated Ge:Sn+P crystals. The electronic structure of Sn-V is unraveled on the basis of hybrid states from a Sn atom and a divacancy. Unlike the case for Si, Sn-V in Ge is not a donor. A hole trap with 0.19 eV activation energy for hole emission to the valence band is assigned to an acceptor level of the Sn-V complex. The Sn-V complex anneals out upon heat-treatments in the temperature range 50–100 °C. Its disappearance is accompanied by the formation of phosphorus-vacancy centers.

Donor levels of the divacancy-oxygen defect in silicon

The elimination of divacancies (V2) upon isochronal and isothermal annealing has been studied in oxygen-rich p-type silicon by means of deep level transient spectroscopy (DLTS) and high resolution Laplace DLTS. Divacancies were introduced into the crystals by irradiation with 4 or 6 MeV electrons. The temperature range of the divacancy disappearance was found to be 225-300 °C upon 30 min isochronal annealing in the samples studied. A clear anti-correlation between the disappearance of V2 and the appearance of two hole traps with activation energies for hole emission of 0.23 eV and 0.08 eV was observed. It is argued that these traps are related to the first and second donor levels of the divacancy-oxygen (V2O) complex, respectively. Significant electric field enhancement of the hole emission from the second donor level of the V2O center occurred in the diodes studied. It is shown that in the range of electric field from 4 × 103 to 1.2 × 104 V/cm the emission enhancement is associated with phonon-assisted t...

Interstitial Carbon Related Defects in Low-Temperature Irradiated Si: FTIR and DLTS Studies

The evolution of radiation-induced carbon-related defects in low temperature irradiated oxygen containing silicon has been studied by means of Fourier transform infrared absorption spectroscopy (FTIR) and deep level transient spectroscopy (DLTS). FTIR measurements have shown that annealing of interstitial carbon atom Ci, occurring in the temperature interval 260-300 K, results in a gradual appearance of a number of new absorption bands along with the well known bands related to the CiOi complex. The new bands are positioned at 812, 910.2, 942.6, 967.4 and 1086 cm-1. It has been found that the pair of bands at 910 and 942 cm-1 as well as another set of the bands at 812, 967.4 and 1086 cm-1 display identical behavior upon isochronal annealing, i.e. the bands in both groups appear and disappear simultaneously. The disappearance of the first group occurs at T = 285-300 K while the second group anneals out at T = 310-340 K. These processes are accompanied by an increase in intensity of the bands related to CiOi. It is suggested that intermediate states (precursors) are formed upon the transformation from a single (isolated) Ci atom to a stable CiOi defect. The results obtained in DLTS studies are in agreement with the FTIR data and show unambiguously the formation of CiOi precursors with slightly lower activation energy for the hole emission as compare to that for the main CiOi state.

Electronic properties and structure of a complex incorporating a self-interstitial and two oxygen atoms in silicon

The electronic properties and structure of a complex incorporating a self-interstitial (I) and two oxygen atoms are presented by a combination of deep level transient spectroscopy (DLTS), infrared absorption spectroscopy and ab-initio modeling studies. It is argued that the IO2 complex in Si can exist in four charge states (IO− 2 , IO02 , IO+ 2 , and IO++ 2 ). The first and the second donor levels of the IO2 complex show an inverted location order in the gap, leading to a E(0/ + +) occupancy level at Ev + 0.255 eV. Activation energies for hole emission, transformation barriers between different structures, and positions of LVM lines for different configurations and charge states have been determined. These observables were calculated by density-functional calculations, which show that they are accounted for if we consider at least two charge-dependent defect structures.

Structure, Electronic Properties and Annealing Behavior of Di-Interstitial-Oxygen Center in Silicon

It is argued in this work that a DLTS signal associated with hole emission from a radiation-induced defect with an energy level at Ev + 0.09 eV is related to a complex of silicon di-interstitial with an oxygen atom (I2O). This signal has been observed in the DLTS spectra of p-type Si:O samples irradiated with either 4-6 MeV electrons or alpha particles. Isochronal and isothermal annealing studies of the samples have shown that the defect responsible for the DLTS signal from the Ev + 0.09 eV level disappears upon heat-treatments in the temperature range 75-100 °C and its formation and annealing behavior is similar to that of a center giving rise to the infrared absorption band at 936 cm-1 previously assigned to a local vibrational mode (LVM) due to the I2O complex. Possible configurations of the I2O complex have been found by ab-initio modeling and analyzed. Formation and binding energies, energy levels and LVMs for different configurations have been determined. It has been found that the minimum energy configuration of the I2O complex consists of the compact I2 to which a divalent interstitial oxygen atom is attached. Calculated values of the strongest LVM (ν = 971 см-1 ) and position of the donor level {Ev + (0.11-0.13) eV} for the minimum energy configuration are very close to those assigned to the I2O defect in the infrared absorption and DLTS experiments.

Formation and annealing of boron-oxygen defects in irradiated silicon and silicon-germanium n+–p structures

New findings on the formation and annealing of interstitial boron-interstitial oxygen complex (BiOi) in p-type silicon are presented. Different types of n+−p structures irradiated with electrons and alpha-particles have been used for DLTS and MCTS studies. Electronic excitation essentially changes the formation rate of BiOi. It has been found that the increase of oxygen content slows the BiOi annealing rate down. The activation energy of the BiOi dissociation has been determined and it was found that germanium doping does not change the activation energy.

Radiation-Induced Defect Reactions in Tin-Doped Ge Crystals

We have recently shown that Sn impurity atoms are effective traps for vacancies (V) in Ge:Sn crystals irradiated with MeV electrons at room temperature [V.P. Markevich et al., J. Appl. Phys. 109 (2011) 083705]. A hole trap with 0.19 eV activation energy for hole emission to the valence band (Eh) has been assigned to an acceptor level of the Sn-V complex. In the present work electrically active defects introduced into Ge:Sn+P crystals by irradiation with 6 MeV electrons and subsequent isochronal annealing in the temperature range 50-300 °C have been studied by means of transient capacitance techniques and ab-initio density functional modeling. It is found that the Sn-V complex anneals out upon heat-treatments in the temperature range 50-100 °C. Its disappearance is accompanied by the formation of vacancy-phosphorus (VP) centers. The disappearance of the VP defect upon thermal annealing in irradiated Sn-doped Ge crystals is accompanied by the effective formation of a defect which gives rise to a hole trap with Eh = 0.21 eV and is more thermally stable than other secondary radiation-induced defects in Ge:P samples. This defect is identified as tin-vacancy-phosphorus (SnVP) complex. It is suggested that the effective interaction of the VP centers with tin atoms and high thermal stability of the SnVP complex can result in suppression of transient enhanced diffusion of phosphorus atoms in Ge.

DLTS Studies of Carbon Related Complexes in Irradiated N- and P-Silicon

DLTS studies of transformation kinetics of different carbon–related complexes in electron irradiated n- and p-type silicon have been performed. It has been found that silicon self-interstitials have very low mobility even at room temperature in p-Si, but become extremely mobile under elec-tron injection. It is shown that upon annealing of interstitial carbon in p-Si a metastable state for interstitial carbon-interstitial oxygen complex is formed. This state has an energy level of about Еv+0.36 eV. The formation of the stable and metastable states takes place concurrently. The observed features of the carbon-related complexes formation are likely related to the existence of different crystallographic orientation of the equiprobable pathways through which the interstitial carbon and oxygen atoms can approach each other.

Formation of Radiation-Induced Defects in Si Crystals Irradiated with Electrons at Elevated Temperatures

Defects induced in silicon crystals by irradiations with 6 MeV electrons in the temperature range 60 to 500 oC have been studied by means of deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS. Diodes for the study were fabricated on n-type epitaxially grown Si wafers. The DLTS spectra for the samples irradiated at elevated temperatures were compared with those for samples, which were subjected to irradiation at 60 oC and subsequent isochronal anneals in a furnace. The dominant radiation-induced defects in the samples irradiated at temperatures lower than 400 oC were found to be vacancy-oxygen (VO) and interstitial carbon – interstitial oxygen (CiOi) complexes. The introduction rates of the VO and CiOi centers increased about twice upon raising the irradiation temperature from 50 to 400 oC. It is argued that this effect is associated with either a) the suppression of the annihilation rate of Frenkel pairs or b) a decrease in the threshold energy for displacement of a host Si atom upon increase in the irradiation temperature. Transformations of deep level traps due to divacancies (V2) and trivacancies (V3) to V2-oxygen and V3-oxygen complexes were found to occur upon irradiation or annealing at temperatures exceeding 250 oC. A clear anti-correlation between changes in the minority carrier life time induced in the p+-n diodes by irradiation at different temperatures and changes in the concentrations of radiation-induced vacancy- and vacancy-oxygen-related complexes was found.

Radiation-induced bistable centers with deep levels in silicon n + – p structures

The method of deep level transient spectroscopy is used to study electrically active defects in p-type silicon crystals irradiated with MeV electrons and α particles. A new radiation-induced defect with the properties of bistable centers is determined and studied. After keeping the irradiated samples at room temperature for a long time or after their short-time annealing at T ∼ 370 K, this defect does not display any electrical activity in p-type silicon. However, as a result of the subsequent injection of minority charge carriers, this center transforms into the metastable configuration with deep levels located at EV + 0.45 and EV + 0.54 eV. The reverse transition to the main configuration occurs in the temperature range of 50–100°C and is characterized by the activation energy ∼1.25 eV and a frequency factor of ∼5 × 1015 s–1. The determined defect is thermally stable at temperatures as high as T ∼ 450 K. It is assumed that this defect can either be a complex of an intrinsic interstitial silicon atom with an interstitial carbon atom or a complex consisting of an intrinsic interstitial silicon atom with an interstitial boron atom.