Statistics and localisation of vertical breakdown in AlGaN/GaN HEMTs on SiC and Si substrates for power applications

• Probability distribution functions of GaN buffer breakdown voltage were determined.
• A time dependent behaviour of vertical breakdown was observed.
• Vertical breakdown paths were localised by backside infrared microscopy.
• The strong localisation of the breakdown paths is due to current filamentation.
• Roles of buffer defects and self-heating effects have been discussed.

We analyse vertical breakdown signatures in normally-off and normally-on AlGaN/GaN HEMTs on Si and SiC substrate for power applications. The probability distribution function of the breakdown voltage VBD values shows mostly a bimodal distribution that is characteristic for substrate/epitaxy type and bias polarity. Different types of distribution functions are tested. The vertical breakdown is found to be a time dependent phenomenon and hypotheses for its initiation are discussed. Using backside infrared microscopy, we found that the breakdown occurs in localized spots, related to current filaments. Failure localisation under pulsed mode shows better spatial localisation compared to the DC conditions.