V. V. Litvinov

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...

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.

Determination of interstitial oxygen concentration in germanium by infrared absorption

The intensities of infrared absorption due to the asymmetric stretching vibrations of interstitial oxygen atoms in Ge crystals enriched with O16 and O18 isotopes have been compared with oxygen concentrations determined by means of secondary ion mass spectrometry. For Ge samples with oxygen content less than 5×1017cm−3, a good correlation has been found between the values of oxygen concentration and the values of the absorption coefficient at the maximum of the Oi16 related absorption band at 855.6cm−1 with a proportionality coefficient CO=1.05×1017cm−2.

Electronic Properties and Thermal Stabilty of Defects Induced by MeV Electron/Ion Irradiations in Unstrained Germanium and SiGe Alloys

Deep states produced during γ irradiation of germanium have been compared with the defects produced by 1 and 3MeV silicon ion implantation. The deep states have been studied using DLTS and Laplace DLTS techniques. Isochronal annealing has been used to investigate the defect evolution and stability over the range 100 to 500°C. It is found that while irradiation damage can be removed with a very low thermal budget, the implantation damage is more complex and much more difficult to remove. By comparing low (1010cm-2) and high (1012cm-2) implantation doses it appears that both the complexity and stability of defects increases with increasing dose. Similar experiments have been performed on Ge rich Si1-xGex (x=0.992). The focus of this work has been on vacancy related defects. It is believed that the diffusion of both acceptors and donors is vacancy mediated in Ge and so vacancy clusters rather than interstitial clusters are expected to be the technologically significant defect in enhanced diffusion. The significance in terms of junction leakage and generation currents are discussed in the paper in the context of the observed defect reactions.

Calibration factor for determination of interstitial oxygen concentration in germanium by infrared absorption

Intensities of infrared absorption due to asymmetric stretching vibrations of interstitial oxygen atoms in Ge crystals enriched with 16O and 18O isotopes have been compared with oxygen concentrations determined by means of secondary ion mass spectrometry (SIMS). For Ge samples with oxygen content less than 5⋅1017 cm-3 a good correlation has been found between the values of oxygen concentration and values of absorption coefficient in maximum of the absorption band at 855.6 cm-1 with a proportionality coefficient CO = 0.95.1017 сm-2. It is argued that kinetics of oxygen-related thermal double donor formation and oxygen loss upon heat-treatments of Ge crystals at 350 оС cannot be described properly with the application of calibration coefficient CO = 5.1016 cm-2, which is widely used for the determination of oxygen concentration in Ge crystals.

Hydrogen-containing donors in silicon: Centers with negative effective correlation energy

The reconstruction of shallow-level hydrogen-containing donors in Si is studied. The donors are formed by implantation of low-energy (300 keV) hydrogen ions into the experimental samples and subsequent heat treatment at 450°C. The experiments are carried out for Ag-Mo-Si Schottky diodes and diodes with a shallow (∼1 μm) p+-n junction. The concentration and distribution of the donors are determined by applying the method of C–V characteristics at a frequency of 1.2 MHz. An analysis of the temperature dependence of the equilibrium electron concentration shows that the reconstruction of the hydrogen-containing donors can be described under the assumption of recharging of a center with negative effective correlation energy (U < 0). The transformation between two equilibrium configurations of a double hydrogen donor (DB++ ↔ DA0) proceeds with the Fermi level position EF = Ec − 0.30 eV. The reconstruction of the donors from a neutral to a doubly charged state (DA0 → DB++) which is stimulated by the capture of minority carriers, is observed at room temperature.

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.

Enhanced formation of thermal donors in irradiated germanium: Local vibrational mode spectroscopy

Oxygen-rich Ge samples were bombarded with fast electrons (E=4 MeV) at 80 °C and subjected to isochronal (100–340 °C) and isothermal (350 °C) annealing. Infrared absorption spectra were measured at room temperature. Preliminary irradiation of the samples is found to strongly enhance the development of the absorption bands in the range 600 to 780 cm−1 when the Ge〈Sb,O〉 crystals are heated to 350 °C. The bands are assigned to local vibrational modes of thermal donors. It is inferred from the annealing studies that a radiation-induced complex with the local vibrational modes at about 770–780 cm−1 is probably responsible for the enhanced growth of the thermal donors. Oxygen dimers are proposed as such a complex.

Formation of hydrogen donors in proton-implanted epitaxial silicon

The formation of shallow hydrogen donors in epitaxial silicon implanted with 300-keV hydrogen ions has been studied at implant doses from 1013 to 6 × 1015 cm−2, using commercial Mo-Si Schottky diodes with the active base region made of epitaxial phosphorus-doped silicon 5 µ m in thickness (ρ = 1.05 and 1.8 Ω cm). The results demonstrate that, at sufficiently high implant doses (F ∼ 1015 cm−2) and temperatures from 350 to 475 °C, there are at least two types of donors, one of which exhibits bistable behavior due to the negative correlation energy of a singly ionized doubly charged donor. At ∼475°C, the bistable H donor is fully annealed, whereas the concentration of stable donors remains unchanged at temperatures from 350 to 475°C. Under fixed post-implantation heat-treatment conditions (350°, 20 min), it is the implant dose that determines which type of H donor will form: at doses in the range 1013 to 1014 cm −2, H donors of the former type are formed, and the maximum in their profile coincides with the projected ion range; implant doses from 1014 to 1015 cm−2 produce H donors of the latter type, and the peak in their profile is located closer to the irradiated surface, in the region of the highest radiation damage.

Donor Center Formation in Silicon Implanted with Hydrogen Ions

We have studied the electrical properties of Schottky diodes based on epitaxial n-Si films irradiated by low-energy (300 keV) hydrogen ions. The implantation of protons at room temperature leads to the formation of shallow donors whose concentration-depth profile coincides with that of the incorporated hydrogen. These donor centers are stable on heating up to 150°C and are completely annealed at a temperature of about 250°C. Heating above 270°C leads to the formation of well-known donor centers with a concentration more than two times that of the centers of the first type. Donors of the second type are annealed in two stages at 375–425 and 450–520°C. The nature of the donor centers of both types is related to the formation and transformation of two-dimensional hydrogen-containing defects in a radiation-damaged crystal.