An improved apparatus for clean surface studies of high resistivity photoconductors

Surface photovoltage phenomena: theory, experiment, and applications

“…The resistance of this Ohmic contact can be rather large without disturbing the measurements due to the large impedance typically present anyway between the two capacitor plates. The measurement of semi-insulating samples is problematic both because a good Ohmic contact is dif®cult to make and because the insulation of the sample mount must be extremely high or the signal is lost through leakage [130]. Furthermore, for a semi-insulating sample the voltage at the free surface of the sample may be different than the voltage applied to the sample electrode due to the potential drop across the sample itself [131].…”

“…Finally, high resistance samples are vulnerable to stray charges and to spurious dielectric response to stray electric ®elds [132]. Thus, while the measurement of high resistance samples is not impossible [130,131], it requires extreme caution.…”

“…To that end, various mechanical arrangements where the probe may be moved away from the sample for the duration of the treatment are usually used [130,141,149,160]. During such sample treatments, the reference electrode must be adequately protected so that its work function does not change.…”

“…A simple precaution against stray capacitance is keeping the sample-to-probe distance, d, constant. Then, the relative difference between CPD measurements of different samples is minimized [130,184]. This may be impractical at liquid surfaces [157] or in the presence of thermal expansion and/or applied stress effects.…”

Designing a Robust Kelvin Probe Setup Optimized for Long-Term Surface Photovoltage Acquisition

“…To find the discharged state, one modulates the capacitance by oscillating the reference electrode perpendicularly to the sample surface. A control loop then feeds back a bias voltage such that the alternating current induced by the vibration is nullified (see, e.g., [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ] for various designs presented over the years).…”