High injection effects on conductivity and carrier lifetime in P-type silicon material

Abstract

High injection changes in carrier lifetime, mobility and density of a semiconductor material are analyzed using the changes in carrier recombination or diffusion processes and in equilibrium of the donor-acceptor centers (including defect centers). The analysis especially involves the variations with carrier injection Δ of state charge q0 and energy level E occupancy state nE(pE) of the material recombination or donor (acceptor) centers, taking into account the Δ, band-gap energy level E, material Fermi-level EF and center capture cross section σ cn,p values. The above variations and high injection changes are then discussed in terms of their effects on the magnitude, rise and decay of the material transient photoresponses of conductivity Δ V(t) and minority carrier diffusion current iD(t). High injection effects on the conditions under which these photoresponses are observed are also pointed out in this paper. With the view of illustrating the above analysis, experimental results are shown which deal with ~ 1 and 10 Ω.cm P-type silicon samples, submitted to Δ ~ 10-3 to 103 × p0 carrier injection by neodymium laser pulses of 55 ns duration. Low dose irradiation by 14 MeV neutrons (9.6 x 1011 n.cm-2) is used to demonstrate the role of material defects in high injection phenomena. Using the comparison between the photoconductivity and minority carrier diffusion current measured responses, the results especially show that acceptor centers are created by the irradiation (E A = Ev + 0.09 eV, σcp = 10-17 cm-2) whose effect is to lower the effects due to the previously existing donor centers (ED ∼ Ec - 0.08 eV, σcn ~ 1.5 × 10-18, in the un-irradiated samples).