Electron-irradiated Ge Research Articles

Thermoluminescence Responses of Photon and Electron Irradiated Ge- and Al-Doped SiO2 Optical Fibres

We carry out a comparison of the thermoluminescence (TL) response of photon and electron irradiated Ge- and Al-doped SiO2 optical fibres, as well as cross-comparison with that of TLD-100. Irradiation is made with 6 MeV electrons and 6 MV photons, for doses ranging from 0.2 Gy to 4.0 Gy. The commercially available Al- and Gedoped optical fibres produce a linear dose-TL response. The TL yield for both of the doped fibres and also for TLD-100 is greater for electron irradiation than for photon irradiation. The TL yield of the Al-doped fibres is a small fraction of that of Ge-doped fibres (by a factor of 25), the Ge-doped fibres offering a response of 59% of that of TLD-100.

Interaction of self-interstitials with oxygen-related defects in electron-irradiated Ge crystals

Electrically active defects induced by irradiation with MeV electrons in oxygen-rich n-type Ge crystals have been studied by means of capacitance transient techniques. Transformation of the defects upon post-irradiation isochronal and isothermal anneals has also been investigated. It is argued that radiation-induced defects with energy levels at 62 ( E 62) and 80 meV ( E 80) below the conduction band edge are associated with complexes of Ge self-interstitials with oxygen-related defects. These complexes are formed upon annealing of electron-irradiated samples at T>50 °C and anneal out at temperatures higher than 140 °C. The activation energy of formation of the dominant E 62 defect has been found to be 0.80 eV.

Electric field enhancement of electron emission from deep level traps in Ge crystals

Effects of electric field on electron emission rates have been studied for a number of deep level traps in electron-irradiated Ge crystals. Static electric fields have been induced by the application of a reverse bias to Au–Ge Schottky barriers. High-resolution Laplace deep level transient spectroscopy has been used to study electron emissions from double acceptor states of the vacancy–oxygen center and vacancy–group-V-impurity atom (Sb or Bi) pairs. It is found that in the range of moderate electric fields [ ( 2 – 5 ) × 10 4 V / cm ] the electric-field enhancement of electron emission from the above traps can be described in the frame of a phonon-assisted tunneling model. This mechanism is characterized by the following dependence of electron emission rate on electric field E: e ( E ) / e ( 0 ) = exp ( E 2 / E ch 2 ) , where E ch is characteristic field strength, which depends on tunneling time τ 2 . The values of E ch and τ 2 have been determined and from the analysis of the values obtained conclusions on the adiabatic potential structures of the traps have been drawn. In the range of low electric fields ( < 2 × 10 4 V / cm ) deviations from the phonon-assisted tunneling mechanism of the electric-field enhancement of electron emission have been observed for the traps studied. It appears that in this range of electric fields the e( E) dependencies can be described in the frame of the Poole–Frenkel mechanism rather than phonon-assisted tunneling.

Defects in electron-irradiated Ge studied by positron lifetime spectroscopy

The formation and annealing behavior of electron-irradiation induced defects in germanium were studied. The undoped Ge samples were irradiated at 4 K with an electron energy of 2 MeV. The fluence was varied between ${10}^{15}$ and ${10}^{19}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}.$ Annealing experiments were performed from 90 K. Additional temperature-dependent positron lifetime measurements after different annealing stages were carried out to make a statement about charge states of defects and to the presence of shallow positron traps. Two main annealing stages were observed. The first between 150 and 250 K was attributed to the annealing of Frenkel pairs. The second annealing stage between 350 and 450 K was observed after irradiation with fluences above ${10}^{17}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ and was assigned to annealing of a complex containing a vacancy and an impurity atom. Furthermore, shallow positron traps were detected after irradiation. This defect type anneals above 330 K in a wide-temperature range.

Positron Annihilation and Profiles of Displaced Atoms in Electron Irradiated Ge

Positron Annihilation and Profiles of Displaced Atoms in Electron Irradiated Ge

Defects in electron-irradiated germanium

Abstract The growth and structure of defects in electron-irradiated Ge has been followed at room temperature and at higher temperatures between 200° and 300°C. At room temperature, small interstitial loops of approximately edge character on {311} planes are observed and eventually grow into dendritic structures. At the higher temperatures, rods elongated along the 〈110〉 directions form first but then tend to widen into plates of interstitial type on {311} planes with a displacement vector R = 0.04〈611〉. It is possible that all of these defects are of the same type and correspond to aggregates of Ge interstitials, but the possibility of impurity effects cannot be ruled out. The defects tend to transform into perfect dislocation loops on annealing.

Surface Effects in Electron-Irradiated Ge at 80°K

Photoconductivity, surface conductance, and Hall and field effect measurements have been made before and after electron irradiations. Before irradiation, both nand p-type specimens show a photoconductive shoulder in the range of photon energies between 0.70 and 0.55 ev, which is connected with a surface effect. Irradiation with energies below the threshold for the introduction of volumne defects (about 400 kev) quenches the photoconductivity in the shoulder and causes an increase in surface conductance in n-type, and a decrease in p-type specimens. 4.5-Mev irradiations (a) extend the shoulder to about 0.49 ev and b) introduce a sharp peak at 0.39 ev. Both features are due to electronic transitions in the surface region. Field effect measurements with steady fields and a superimposed alternnting potential indicate that the shoulder is connected with transitions from the valence band into a group of slow surface states lying between 0.70 and 0.58 ev above the valence band. Irradiation below 400 kev increases the surface potential Y until, in n-type specimens, the Fermi level pases through a high concentration of fast states within 0.05 ev of the conduction band. 4.5-Mev irradiations decrease Y; transitions to a second group of slow states lying between 0.4 and 0.2 evmore » above the valence band can now take place. (auth)« less