Influence of gamma-radiation on properties of zirconium levels in silicon

Full text: The behavior of materials at irradiations depends substantially on nature and concentration of impurity interacting with primary radiation defects. It is of significant interest to study irradiation effect on crystals in which besides the basic impurity, another active impurity generates deep levels in the forbidden zone, effectively interacting with radiation defects. In the given work we used the method of non-stationary capacitor spectroscopy (DLTS) influence of gamma- irradiation on properties of levels of zirconium in silicon is studied. The samples were irradiated by 60Co gamma-quanta at the dose rate of 3.4x1012 q/cm2xs. It was revealed, that doping of Si with Zr by diffusion leads to formation of three deep levels (DL) with fixed ionization energy: Ec-0.22 eV, Ec-0.42 eV and Ev+0.30 eV, and the last prevails two DL. As seen from DLTS, the gamma-irradiation does not have noticeable influence on DL parameters of n-Si . Measurement of doze dependences of DL concentration (Nt) in the 'oxygen' silicon doped by zirconium have shown, that changes of concentration Nt in the investigated interval of irradiation dozes have nonlinear character and depend on the initial DL concentration. The analysis of DLTS spectra has shown, that after gamma - irradiations a new level with ionization energy of Et= Ec-0.17 eV and cross-section of capture electrons σn ∼1014 sm2 is entered. Values of energy of ionization Et and sections of electron capture σn for this level coincide with the parameters of the oxygen - vacancy complex (A- center). The concentration of this defect depends on an irradiation doze non-linearly. Study of the control samples has shown, that the -quanta-irradiations generated A - centers in them too. However the doze dependence of this center concentration is linear, unlike the dependence in the doped samples. Besides the generation rate of A - center in the control samples at F ∼1017 q/cm2xs is more than in n-Si (and, in initial heat treatment control samples it differs slightly). Concentration of other DL in the control samples after the irradiation is <5x1011 cm-3. We also investigated features of radiation defect formation in the 'oxygen-free' silicon doped by zirconium. Measurements of DLTS spectra of control samples of 'oxygen-free' silicon have shown, that besides A- centers the gamma- irradiation generates one more characteristic radiation defect E-center with the ionization energy of Ec-0.43 eV and electron capture cross-section of σn =1.8x10-15 cm-2. E-center concentration in these samples at the irradiation doze 8x1017 q/cm2xs makes 5.3x1013 cm-3, and A- center concentration is 3x1013 cm-3 which is less than that in 'oxygen' silicon. After a low dose irradiation of the samples doped by zirconium, E-centers are not observed, but after a higher doze the DL concentration with Ec-0.43 eV decreases. (authors)