Wavelength-dependent switching of photocurrent polarity in a semiconductor film with bifacial band bendings

We have found that a semiconductor film with bifacial band bendings formed in the same direction exhibit a bipolar photocurrent response that depends on the incident light wavelength. A device simulation indicated that the barrier heights and directions of the band bendings were essential factors in the wavelength-dependent bipolar outputs. Interestingly, the transition wavelength of the output polarity can be tuned by changing the film thickness. We experimentally revealed that single crystalline n -type tungsten disulfide, for which the front and rear surfaces were modified, exhibits a wavelength-dependent bipolar output.