A new technique for depth resolved carrier recombination measurements applied to proton irradiated thyristors

A contactless technique for localized carrier recombination measurements is demonstrated and applied for depth resolved lifetime measurements of proton irradiated thyristors. The measurement principle is based on homogeneous generation of carriers by a laser pulse and the simultaneous detection of carriers using free carrier absorption of a focused infrared probe beam. The new approach relies on the instantaneous detection of the build-up of carriers during a short excitation pulse for which diffusion effects become negligible. By comparing the measured number of carriers in a defect laced sample with the optical generation rate during the pulse, e.g., inferred from the number of generated carriers in a virgin Si sample, the lifetime is calculated. The technique has been applied on proton irradiated thyristor structures where the resulting carrier recombination depth profiles show good agreement with Monte Carlo simulated ion damage profiles. In particular, the damage tail towards the surface is clearly resolved. This shows that defects created in the proton tracks are electrically active and need to be considered for proper device performance. Annealing studies show that active recombination centers, created by the proton irradiation, are relatively stable up to 300 C whereas < 20% of the centers remain at 400 C. These annealing characteristics and the excellent correlation between carrier recombination profiles and calculated proton vacancy distributions suggest that the main defects controlling the recombination are vacancy related, most probably divacancies