Noninvasive optical probe of free charge and applied voltage in GaAs devices

We have demonstrated an application of a noninvasive optical probe that can independently measure both free sheet charge density and applied voltage in GaAs devices. Large-signal direct-current measurements of voltage and charge were made on a Schottky diode without any assumption of the device parameters. The measurements are reproducible, and no adjustable parameters have been used to quantitatively measure charge and voltage. In addition to a lateral charge resolution, given by the beam spot size, we have observed a longitudinal resolution due to the standing wave in the probe beam.