When testing a wavelength light that is shorter than the absorption wavelength of P-N linked semiconductor, it is found that light with more energy than that of semiconductor¡¯s band gap is absorbed into the semiconductor and create electron-hole pairs. Finally, an expanded potential difference occurs.
Electrons and holes that are generated by a light test will have electromotive forces on both sides, which are caused by drift effect. This effect is called ¡®photovoltaic effect¡¯.