Papers by Author: Valentin V. Litvinov

Abstract: 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 (E_h) 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 E_h = 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.

Abstract: It is found that shallow hydrogen-related donors are formed in proton-implanted dilute Ge1-хSiх alloys (0 ≤ x ≤ 0.031) as well as in Si-free Ge samples upon heat-treatments in the temperature range 225-300oC. The maximum concentration of the donors is about 1.5×1016 cm-3 for a H+ implantation dose of 1×1015 cm-2. The temperature range of formation of the protonimplantation- induced donors is the same in Ge1-xSix samples with different Si concentration. However, the increase in Si content results in a decrease of the concentration of the hydrogenrelated donors. It is argued that the H-related donors could be complexes of Ge-self-interstitials with hydrogen atoms. The observed decrease in the concentration of the donors with an increase in Si content in the Ge1-xSix samples is associated with interactions of mobile hydrogen atoms with Si impurity atoms. Such interactions reduce the number of implanted hydrogen atoms that can be involved in defect reactions resulting in the formation of H-related shallow donors.

Abstract: 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.

Abstract: 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.

Abstract: The transformation of the shallow hydrogen-related donors, which have been formed in the silicon samples by irradiation of the low energy (300 keV) protons and following heat treatment under 350 0С or 450 0С was investigated. The experiment was carried out on Ag-Mo-Si Shottky diodes and diodes with shallow p+-n-junction. The concentration and distribution of these donors were defined by C-V-method at 1.2 MHz frequency. Using temperature dependence of equilibrium electron concentration it was established, that the hydrogen-related donors were charged controlled centers with negative electronic correlation energy (U<0). The transformation between both equilibrium configurations of the double hydrogen-related donor takes place when value of the Fermi level is arranged near Ec-0.30 eV. It was revealed that the donor transformation from neutral into double charged state have been stimulated by minority carriers trapping under room temperature when Fermi level was higher then level of the double electron occupation E(0/++)= Ec-0.30 eV.