V.P. Markevich

Electronic properties of antimony-vacancy complex in Ge crystals

Schottky barriers formed by depositing Au on n-type Ge have been used to study the antimony-vacancy complex (E center). Both hole and electron transitions have been observed because the formation of an inversion layer at the semiconductor surface enables minority carriers to be injected when the Schottky barrier is forward biased. It is argued that the E center in Ge has three charge states: double negative, single negative, and neutral. The free energy of electron ionization for the double acceptor level of the complex has been found to be ΔG(=/−)=0.294−4.2 kT (eV), where k is Boltzmann’s constant. Consequently, the position of the double acceptor level of the E center {E(=/−)=Ec−ΔG(=/−)} is temperature dependent. In moderately Sb-doped (NSb=1013–1015 cm−3) Ge crystals at equilibrium conditions half-occupancy of the double acceptor state of the Sb-V complex occurs when the Fermi level is at about Ec−0.20 eV. The single acceptor level of the E center is in the lower part of the band gap. The activation en...

Electronic properties of vacancy–oxygen complex in Ge crystals

It is argued that the vacancy-oxygen (VO) complex (A center) in Ge has three charge states: double negative, single negative, and neutral. Corresponding energy levels are located at E-c-0.21 eV (VO--/-) and E-v+0.27 eV (VO-/0). An absorption line at 716 cm(-1) has been assigned to the asymmetrical stretching vibration mode of the doubly negatively charged VO complex

The oxygen dimer in Si: Its relationship to the light-induced degradation of Si solar cells?

It is widely believed that the light induced degradation of crystalline silicon solar cells is due to the formation of a BsO2i recombination center created by the optically excited migration of the oxygen dimer (charge-state-driven motion). In this letter the concentration dependence of the neutral state of O2i on [Oi] in p- and n-type Cz–Si has been determined using infrared absorption. A systematic search for the absorption signature of the dimer in the doubly positively charged state has been unsuccessful. These data strongly suggest that charge-state-driven motion (Bourgoin–Corbett mechanism) of the oxygen dimer cannot occur in typical solar silicon and hence bring into question the accepted degradation mechanism.

Defect reactions associated with divacancy elimination in silicon

Defect reactions associated with the elimination of divacancies (V-2) have been studied in n-type Czochralski (Cz) grown and float-zone (FZ) grown Si crystals by means of conventional deep-level transient spectroscopy and high-resolution Laplace deep-level transient spectroscopy (LDLTS). Divacancies were introduced into the crystals by irradiation with 4 MeV electrons. Temperature ranges of the divacancy disappearance were found to be 225-275 degreesC in Cz Si crystals and 300-350 degreesC in FZ Si crystals upon 30 min isochronal annealing. Simultaneously with the V-2 disappearance in Cz Si crystals a correlated appearance of two electron traps with activation energies for electron emission 0.23 eV {E(0.23)} and 0.47 eV {E(0.47)} was observed. It is argued that the main mechanism of the V-2 disappearance in Cz Si crystals is related to the interaction of mobile divacancies with interstitial oxygen atoms. This interaction results in the formation Of V2O centres, which are responsible for the E(0.23) and E(0.47) traps. Electronic properties of the V2O complex were found to be very similar to those of V-2 but energy levels of the two defects could easily be separated using LDLTS. In FZ Si crystals, a few electron traps appeared simultaneously with the V-2 annihilation. The small concentration of these traps compared with the V-2 concentration before annealing prevented their reliable identification. (Less)

Defect engineering in Czochralski silicon by electron irradiation at different temperatures

Infrared absorption studies of defect formation in Czochralski silicon irradiated with fast electrons in a wide range of temperatures (80-900 K) have been performed. The samples with different contents of oxygen (O-16, O-18) and carbon (C-12, C-13) isotopes were investigated, The main defect reactions are found to depend strongly on irradiation temperature and dose, as well as on impurity content and pre-history of the samples. Some new radiation-induced defects are revealed after irradiation at elevated temperatures as well as after a two-step (hot + room-temperature (RT)) irradiation.

Gettering of interstitial iron in silicon by plasma-enhanced chemical vapour deposited silicon nitride films

It is known that the interstitial iron concentration in silicon is reduced after annealing silicon wafers coated with plasma-enhanced chemical vapour deposited (PECVD) silicon nitride films. The underlying mechanism for the significant iron reduction has remained unclear and is investigated in this work. Secondary ion mass spectrometry (SIMS) depth profiling of iron is performed on annealed iron-contaminated single-crystalline silicon wafers passivated with PECVD silicon nitride films. SIMS measurements reveal a high concentration of iron uniformly distributed in the annealed silicon nitride films. This accumulation of iron in the silicon nitride film matches the interstitial iron loss in the silicon bulk. This finding conclusively shows that the interstitial iron is gettered by the silicon nitride films during annealing over a wide temperature range from 250 °C to 900 °C, via a segregation gettering effect. Further experimental evidence is presented to support this finding. Deep-level transient spectrosc...

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.

Vacancy–oxygen complex in Si1−xGex crystals

Electronic properties of the vacancy–oxygen complex in unstrained Si1−xGex crystals (0<x⩽0.055) grown by the Czochralski method were studied by means of capacitance transient techniques. The enthalpy of electron ionization for the single acceptor level of the defect relative to the conduction band edge, ΔHn, was found to increase from 0.16 to 0.19 eV with the increase in Ge content. The change of the lattice parameter in Si1−xGex alloys is argued to be one of the main reasons of the observed ΔHn change.

VOn (n >= 3) defects in irradiated and heat-treated silicon

Local vibrational mode (LVM) spectroscopy has been used to study the evolution of vacancy-oxygen-related defects (VOn) in the temperature range 300-700°C in carbon-lean Cz-Si samples irradiated with MeV electrons or neutrons. New experimental data confirming an attribution of the absorption bands at 910, 976 and 1105 cm-1 to the VO3 complex are obtained. In particular, a correlated generation of VO3 and the oxygen trimer is observed upon irradiation of Cz- Si crystals in the temperature range 300-400°C. Strong evidence for the assignment of the bands at 991 and 1014 cm-1 to a VO4 defect is presented. The lines are found to develop very efficiently in the VO2 containing materials enriched with the oxygen dimer. In such materials the formation of VO4 is enhanced due to occurrence of the reaction O2i+VO2 ⇒ VO4. Annealing of the VO3 and VO4 defects at T ≥ 550C °C is found to result in the appearance of new defects giving rise to a number of O-related LVM bands in the range 990-1110 cm-1. These bands are suggested to arise from VO5 and/or VO6 defects. Similar bands also appear upon the annihilation of oxygen-related thermal double donors at 650°C in Cz-Si crystals pre-annealed at 450°C.

Energy state distributions of the Pb centers at the (100), (110), and (111) Si∕SiO2 interfaces investigated by Laplace deep level transient spectroscopy

The energy distribution of the Pb centers at the Si∕SiO2 interface has been determined using isothermal laplace deep level transient spectroscopy. For the (111) and (110) interface orientations, the distributions are similar and centered at 0.38eV below the silicon conduction band. This is consistent with only Pb0 states being present. For the (100) orientation, two types of the interface states are observed: one similar to the (111) and (110) orientations while the other has a negative-U character in which the emission rate versus surface potential dependence is qualitatively different from that observed for Pb0 and is presumed to be Pb1.