DIELECTROPHORESIS DEVICE

Provided is a variable conductivity film exhibiting a large change in conductivity so as to facilitate movement or sorting of micro-materials. Silicon semiconductor layers disposed between a first electrode and a second electrode include: a first silicon layer of a first conductivity type with a first impurity concentration; a second silicon layer of a second conductivity type different from the first conductivity type, contacting the first silicon layer and having a second impurity concentration smaller than the first impurity concentration; and a third silicon layer of the first conductivity type contacting the second silicon layer and having a third impurity concentration larger than the second impurity concentration. The first silicon layer and the second silicon layer form a first photodiode having a first polarity, and the second silicon layer and the third silicon layer form a second photodiode having a second polarity and being connected in series to the first photodiode.