CONTACTLESS FREQUENCY RESOLVED PHOTOCONDUCTANCE (FR-PC) MEASUREMENT OF IRON CONTAMINATED P-TYPE SILICON

摘要

The temperature dependence of the minority carrier lifetime and the surface recombination velocity have been measured in p-type Si wafers containing 10~(11)cm~(-3) Fe, using Frequency Resolved Photoconductance (FR-PC) method. The recombination trapping centers have been identified from the microwave signals drawn as Nyquist plots. Changing the temperature and dc injection level enables one to characterize the traps with the nonlinear simplex fitting procedure. Under moderate dc injection level the Nyquist plots exhibit a large arc over the temperature range 24°C to 240°C. For low dc injection, and at temperatures below 100°C, the principal arc is deformed giving rise to second arc. However, this deformation and the second arc disappear above 180°C. Optimum fitting procedures show that the principal arc is associated with carrier recombination due to interstitial Fe_i, while the arc deformation is attributed to electron trapping at this level. The second arc can not be fitted by the above models; however, the Lorentzian amplitude and peak dependence on dc injection level leads us to believe that another level, donor Fe-B, is involved in electron trapping. Observed discrepancy at the room temperature between the effective lifetime and the frequency resolved lifetime is attributed to this level. Above 180°C both lifetimes correlate perfectly.