An ITO/a-Si:H Schottky Photodiode(PD) with Mo as a barrier metal at Al/ITO contact has been made and it shows its useful characteristics. The PD without Mo had high dark current proportional to the contact-via-hole area and quite a large resistance at the contact area. The XPS analysis of the Al/ITO interface indicated that Al and O in ITO mutually diffused around the interface, resulting in the degradation of ITO/a-Si:H Schottky barrier. Most of the diffused Al formed aluminum oxide (AI2O3) at the Al/ITO interface, and which caused high resistance of the contact area.
Inserting Mo barrier metal 500Å thick, the dark current got less dependent on the contact area and decreased by 2/3 on 254×227 μm PD with 106×106//m contact-via-hole. The contact resistance also decreased significantly to 1/105 of those of the conventional ones. From the XPS analysis of interface, it was also found that Mo barrier metal prevented Al diffusion into the ITO and formation of aluminum oxide at the interface.