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β-FeSi2 has many attracting properties as a semiconductor not consisting of toxic chemical elements and is an
ideal semiconductor as a thin film solar cell owing to its extremely high optical absorption coefficient. To evaluate
β-FeSi2 as a solar cell, photo-response measurement is critically important and useful. Since β-FeSi2 thin films are
normally deposited on Si substrates, intrinsic photo-response of β-FeSi2 is usually difficult to be collected due to the
strong contribution from Si substrates. We here present the photo-response from bulk β-FeSi2 crystals, expecting that we
can eliminate the contributions coming from the Si substrates and the crystallographic defects existing at the β-FeSi2/Si
interfaces when we use β-FeSi2 thin films. We prepared bulk specimens by chemical vapor transport method (CVT) in
which needle-like and plate-like β-FeSi2 crystals were obtained. We chose the former specimens for the formation of
Al/n-β-FeSi2 Schottky contacts to measure their photo-responses. These contacts were found to form Schottky diodes
even though there are large series resistances and leakage currents. Under laser light illumination of 1.31 μm through
optical fiber, the positive voltage was observed between the Al contact and the In solder glued to the back-surface of
β-FeSi2 bulk specimen. Two-dimensional distribution of photo-responses were measured by scanning the above optical
fiber with the spot size of 50 μm. The highest photo-response was obtained in the vicinity of Al wire, and was 7.7 mA/W
for the as-grown sample, and 31 mA/W for the annealing one, respectively. These observations state that β-FeSi2 holds
appropriate optical features to be used as a solar cell.
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