We have succeeded in enhancing the photovoltaic properties of p-n heterojunctions using β-FeSi 2/Si(1 0 0) by doping Al into β-FeSi 2. Raman spectroscopy, Rutherford backscattering spectroscopy (RBS) and transmission electron microscope (TEM) observations revealed that Al doping contributes to the synthesis of a less defective interface and epitaxial growth of β-FeSi 2 on Si(1 0 0). This feature of epitaxial growth may reduce the recombination rate of electron-hole pairs near the depletion region, such that the photoresponse can be enhanced. We observed a significant photoelectric response corresponding to the interband transition near the band-gap energy of β-FeSi 2. This effect of the Al doping can be used in IR-photoelectric cells.