Improved lifetime characteristics in heavy ion irradiated silicon

Silicon samples of various doping concentrations have been irradiated with MeV ions at low doses and different temperatures. Deep level transient spectroscopy (DLTS) has been used to characterise the distributions and productions of the divacancy center (V 2 ) and the vacancy-oxygen complex (VO). These two defects have been identified as being responsible for the charge carrier lifetime reduction. Due to their bandgap position and capture cross sections the singly negative charge state of the V 2 controls the low level injection lifetime, but the influence of VO becomes stronger for higher injection levels. The relative abundance of the two defects can be affected by using heavier ions than protons and electrons, which are commonly used today in the fabrication of silicon power devices. The reason for this is that the production of V 2 is enhanced by larger collision cascades, in comparison to VO, following heavier ion implantation. It will be shown that irradiation with heavy ions, instead of protons and electrons, will result in a better relationship between the high and the low level lifetime. This effect can be taken advantage of to improve the trade off between switching time and conduction losses in power devices. It will also be shown that the concentration ratio VO/V 2 can be further improved if the irradiations are performed at lower temperatures than room temperature.