Influence of growing and doping methods on radiation hardness of n-Si irradiated by fast-pile neutrons

Abstract

Silicon n-type samples with resistivity ~2.5⋅10 3 Ohm⋅cm grown by the method of a floating-zone in vacuum (FZ), in argon atmosphere (Ar) and received by the method of transmutation doping (NTD) are investigated before and after irradiation by various doses of fastpile neutrons at room temperature. The radiation hardness of n-type silicon is shown to be determined first of all by the introduction rate of defect clusters and their parameters and then by the introduction rate of defects into the conducting n-Si matrix. The presence of oxygen, argon atoms and A-type defects (dislocation loops of the interstitial type) mainly increases the radiation hardness of n-Si. The effective concentration of carriers in irradiated silicon was calculated in the framework of Gossicks model taking into account the recharges of defects both in the conducting matrix of n-Si and in the space-charge regions of defect clusters. Grown by the method of the floating-zone melting in argon atmosphere the neutron-transmutation-doped silicon (NTD) has elevated radiation hardness. The introduction rate of divacancies in the conducting matrix of n-Si (NTD) is about five times less than in n-Si (FZ) and ~2 times less than in n-Si (Ar). The availability of the deformation strain field surrounding the argon-type impurities as well as A-type defects is supposed to promote the annihilation of divacancies with interstitial atoms of silicon.

The radiation hardness of pulled silicon doped with germanium

“…where N 2 (T, Φ ) is the concentration of screening centres in space-charge regions (SCRs) of defect clusters; ε, ε 0 are the dielectric constants of material and vacuum, respectively; µ is the Fermi level position relative to the conduction band bottom in a cluster; N c (T) is the effective state density in the conduction band. In more detail this technique is described in [13].…”

“…Let neutrons create uniformly distributed point acceptor defects in n-Si volume (except for disordered regions) with the concentration N a < N d . Then, with increase of the sample temperature from 77 K the thermal excitation (ionization) of carriers from E a level gives some electron concentration in the conduction band both in the conducting matrix n(T, Φ ) and in SCRs of defect clusters 4.0x10 13 6.0x10 13 8.0x10 13 1.0x10 14 1.2x10 14 t, s n cl , cm -3…”

“…1.0x10 13 3.0x10 13 5.0x10 13 7.0x10 13 T ann = 353 K n cl , cm -3 T where g = 2 is the degeneration factor of the acceptor level; N a ( Φ ) is the concentration of radiation-induced acceptor defects after fluence Φ ;…”

“…In the improved model of defect clusters, it was supposed that in intrinsic silicon the Fermi level is situated at the neutral level of the divacancy (E v +0.52 eV, in our estimations). When a free electron is captured, the energy of V 2 centre will increase by 0.165 eV [13]. Therefore, with increasing the dopant concentration the Fermi level in cluster will be shifted to the conduction band.…”

“…In its turn, this can lead to more effective annealing of defects in clusters and to decreasing R 1 . But other mechanism of the influence (for example, the deformation mechanism) of 14 1.9×10 14 0.078 0 3×10 13 5.23×10 14 V (Е с −0.49 eV) in the forbidden band. According to [15], in Cz-Si the (Е c −0.45 eV) slope describes the combined effect of acceptor levels of divacancy and trivacancy in the conducting matrix.…”