Influence of thermal processing on life-time of charge carriers in silicon doped by nickel

Full text: This work is devoted to research on influence of thermal processing on electrophysical and recombination properties of n- and p-type silicon doped by nickel, in particular, electronic and hole processes depending on degree of metastability of the material. The studies were performed using a set of techniques such as the deep level transient spectroscopy (DLTS) measurements on Schottky diodes, measurements of Hall coefficient and life-time of charge carriers using stationary photoconductivity technique, thermal diffusion technique for doping of n- and p-type silicon by nickel, as well theoretical analysis. The important results obtained are follows: The electrical levels E1=Ec - 0.21 eV and E2=Ec - 0.42 eV were identified in the fast cooled samples, at this the concentration of the level E2 is almost two time smaller than that of the level E2 and does not depend on post-diffusional cooling rate. The levels E1 and E2 can be attributed rather complexes of [Ni+I] than to substitutional Ni. In p-Si samples cooled slowly (I) and fast (II), the acceptor level Ev+0.35 eV was identified. The concentration of this level depends on the post-diffusional cooling rate; it is almost two times higher in I-type samples than that in II-type samples. The increase in concentration of compensating nickel centers (Ev+0.35 eV) leads to decrease of mobility, μ, and life-time, τ, of charge carriers (at T=300 K), at this relative decrease of μ higher (1/τ lower) in I-type samples as compared to II-type samples. This fact can be explained by different degree of micro-inhomogeneity of conductivity of these samples. It was revealed decrease of observed centers (E1and E2) up to annealing temperature of ∼250 deg. C. In the II-type samples we observed additional deep level centers (Ec - 0.32 eV and Ec - 0.5 eV) in the annealing temperature range of 120-310 deg. C. These levels strongly influence on life-time of minority charge carriers. At the maximal concentration of nickel in silicon the life-time of minority charge carriers is 5 times larger in I-type p-Si samples than that in Il-type samples. Character of changes of life-time of charge carries was found to be quite different for I- and Il-type samples at isochronal annealing. In particular, thermal stability of life-time in the II-type samples was observed up to temperatures ∼250-300 deg. C, while in the I-type samples it increases in the temperature range of 150-230 deg. C, which may be due to annealing of uncontrollable impurities (at this concentration of nickel is not annealed). This work was supported by the Fund for Supporting Fundamental Researches of Uzbekistan Academy of Sciences, Grant No 10-04