IMPS/IMVS capabilities video

Many semiconductor characterization techniques involve static material perturbations. For example, one can apply a DC bias potential and observe resulting (not necessarily constant) electric current. Or application of light intensity fixed in time can reveal the efficiency of the sample in producing photocurrents.

An entirely new world of phenomena opens when one starts varying the stimulus in time. If we let bias potential to be periodic in time the impedance spectroscopy
is born. In the modern time-resolved form this is utilized in Impedance Cameras.

On the other hand if the incident monochromatic light is modulated the Intensity Modulated Photocurrent Spectroscopy (IMPS) or Intensity Modulated Photovoltage Spectroscopy (IMVS) arises. The first technique is performed at short circuit conditions, where electric current is measured. The second one, at an open circuit, where voltage created by the light is explored.

By varying if the light intensity modulation frequency one can determine the quantities like:

• transport time from the front to the back side of the sample with IMPS

• recombination rate or minority carrier lifetime with IMVS

• diffusion constant determining transport of photocurrent mediating carriers

• diffusion length of those carriers

• charge capture efficiency that summarizes the interplay of diffusion and recombination into a single quantity relevant to the harvesting energy from the device.