Test of the thermal equilibration model for persistent photoconductivity in doping-modulated amorphous silicon.
The persistent photoconductivity effect in doping modulated amorphous silicon is compared to the light-induced conductivity changes in compensated amorphous silicon. The recent proposal that the defect structure of doped amorphous silicon is in metastable thermal equilibrium is able to account for the metastable excess conductivity in both systems, and for the several orders of magnitude difference in exposure times needed.
Time-of-flight studies of compensated a-Si:H
Abstract The drift mobility and charge collection of compensated a-Si:H are measured using time-of-flight photoconductivity. The mobility of both electrons and holes decreases rapidly as the doping level is increased. From the results we suggest that shallow traps arising from boron-phosphorus complexes are introduced. The charge collection measurements demonstrate that compensated samples of a-Si:H have a low dangling bond density.
Measuring Sheet Resistances of Dielectrics Using Co‐Planar Hydrogel Electrochemical Cells with Practical Applications to Characterize the Protective Quality of Paints on Sculptures
Electrical properties of thin dielectric films at the solid-liquid phase boundary are an important performance characteristic of many devices, coatings and sensors. In this paper, co-polymeric hydrogels of polyacrylic acid co-sulfonic acid, swollen with a salt solution to act as the solid electrolyte, were used to assess interfaces using electrochemical impedance spectroscopy (EIS) in a co-planar geometry. Silane-modified glasses were characterized by the co-planar hydrogel EIS cell and found to be distinguishable based on their surface monolayer chemistry. EIS measurements were also made on primed and painted metal substrates, using both test panels and an outdoor sculpture, Tony Smith's Stinger. The panels were then exposed to accelerated and outdoor weathering and showed degradation on the surface paint layers, which was observable electrochemically using EIS and confirmed visually by SEM. Electrochemical spectral features were compared between data from a standard paint-test cell versus this co-planar hydrogel cell; both cell types were able to measure coating capacitance, providing useful information about the condition of the bulk coating. Yet, sheet resistance (Rs) was a spectral feature seen only by the co-planar hydrogel cell. Thus, it can be concluded that the use of such co-planar hydrogel cells can provide an earlier warning sign to coating degradation and such cells provide a new type of spectral information that is not assessable by the standard geometry.