Photoemission Measurements of Schottky Energy Barriers

1 Internal Photoemission Measurements of Schottky Energy Barriers 

These Schottky energy barriers are measured in the presence of an electric field in the structure which is necessary to be able to collect the photocurrent. The photocurrent thresholds are not the zero electric field Schottky barriers because of the electric field in the polymer and the image charge potential created when the electron leaves the metal. This effect results in a lowering of the Schottky energy barrier given by [34] 

It is difficult to measure metal/polymer Schottky energy barriers smaller than about 0.5 eV using internal photoemission. Small Schottky energy barriers lead to thermal emission currents produced by the absorption of light in the metal which are difficult to separate from true photocurrents [34]. If the structure is cooled to try to improve this contrast, it is often found that the significant decrease in the electrical transport properties of the polymer [27] makes it difficult to measure the internal photoemission current. To overcome this limitation, internal photoemission and built-in potential measurements are combined to measure small Schottky energy barriers, as described below. 

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