Analysis of n⁺ p silicon junctions with varying substrate doping concentrations made under ultraclean processing technology

Using highly controlled ultraclean processing technology, marked improvements in n⁺ p Si junction quality are achieved presenting a theoretical significance. Boron-doped substrates with various boron doping concentrations N_s were As⁺ implanted, forming the n⁺ junction sides. The diffusion (I_d) and generation (I_gen) currents, as well as the ideality and the generation factors, are significantly reduced, and bulk generation lifetimes are prolonged. Using Shockley-Read-Hall theory it is found that a deviation of the trapping centers energy (E_t) from the midband-gap energy (E_i) is responsible for the improvements. The experimental results show that |E_t - E_i| is a function of N_s, and that the I_gen/I_d ratio is significantly low. Accordingly, it is proposed that I_gen/I_d ratio should be regarded, under certain conditions, as a figure of merit for junction quality. It is concluded that the |E_t-E_i| deviation is related to the ultraclean processing technology used, due to the formation of new energy levels far from E_i and the suppression of introduction of new energy levels near E_i. Surface generation currents were found experimentally to be significant, and thus not negligible. Surface effects in general demonstrated similar trends to the bulk generation effects.