Curious conductance

13 02 2011

The conductance data from the aged capacitors is throwing up a number of interesting surprises. It’s strange, but it is often considered to be the poor cousin of the capacitance – voltage characteristic, however it would appear that there’s plenty to discover in here and not all of it appears to be described in the literature. The first observation is that the amplitude of the peak can be used to describe the interface trap density, Dit, using the HIll – Coleman technique. (although this generally underestimates Dit, this is the technique everyone uses in SiC) That for most people is the end of the story …

The position of the peak is often considered to be related to the position of the trap in the band gap and this is where the observations began. Our recent data suggests that this position is also related to the shift in flat band voltage, with the peak occurring at Vfb. This would indicate that we have a consistent trap in our data sets, rather then one which moves within the bandgap. From there we started to investigate the make up of the conductance peak and found that it cannot be described by a single Gaussian function, which makes me suspect we have multiple trapping states contributing to the signal. We also noticed that the full width half maximum (FWHM) of the dominant Gaussian increases as the device starts to fail (defined as a large increase in leakage current) in a linear manner. This is something new for us and has us scratching our heads and going back to the books. If anyone can point us in the right direction here, give us a shout!

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