IN-SITU MEASUREMENTS OF CHANGES OF THE EXCESS CHARGE-CARRIER DECAY-RATE AT THE CRYSTALLINE SILICON SURFACE DURING LOW-TEMPERATURE ANNEALINGAND COOLING

The transient photoconductivity decay rate is monitored on crystalline silicon samples in-situ during the heating of the samples up to 250 d egrees C and subsequent cooling by measuring the changes in the microw ave reflection of the silicon sample following laser pulse illuminatio n. An irreversible change of the excess charge carrier lifetime is fou nd, showing a much slower decay after the first heating to 250 degrees C. Subsequent thermal cycles show only a weak temperature dependence of the excess charge carrier decay rate at different temperatures. The strong dependence of this effect on the wavelength of the exciting la ser indicates that the effect is caused by a modification of a near su rface region of the crystalline silicon. The dependence of the signal amplitude on the measurement temperature is used to derive the tempera ture dependence of the sum of the electron and hole mobilities in the crystalline silicon.