Novel Noncontact Approach to Monitoring the Field-Effect Passivation of Emitters

We report a comprehensive noncontact approach to measurement of the field-effect passivation of emitters for p and n-type base silicon solar cells. The corona charge-voltage technique, extensively used in silicon IC fabrication lines, is utilized in an automated sequence with two complementary measurements that monitor charge induced changes of recombination in the emitter. Quasi-steady-state microwave photoconductance decay, QSS-μPCD measures decay lifetime τeff, the injection level, Δn and the emitter saturation current, J0. UV and blue ac-surface photovoltage (UV-SPV) gives a passivation indicator analogous to short wavelength quantum efficiency. Field-effect characteristics of τeff, Seff, J0, and UV-SPV are presented for symmetrical n + and p + emitter test wafers that quantify the effect of charge, polarity and differences between n + and p + emitters. New findings include field effect hysteresis and charging induced emitter degradation phenomenon analogous to stress induced degradation in MOS devices.