Thermal Cycle Degradation of Charge Carrier Lifetime and Resistivity in Silicon

Numerous published examples of high temperature induced changes in the properties of semiconductors indicate that thermal degradation of charge carrier lifetime may be responsible for excess current and noise in diffused junction radiation detectors. By comparing the noise and current in surface barrier diodes made from silicon which had been subjected to a thermal cycle to the properties of similar diodes made from uncycled material, it is demonstrated that there can be severe degradation of the original material. The relationship between charge carrier lifetime and noise in semiconductor radiation detectors is discussed. Detailed information on changes in resistivity and etch pit density for both p- and n- type silicon from several manufacturers as a function of original resistivity and thermal cycle is presented. Information on excess diode current and noise is available only for the n-type samples. The results are consistent with the previously observed strong dependence on both maximum temperature and rate of temperature change. Large increases in diode current and noise have been observed for cycles with peak temperatures as low as 500°C.