A one-dimensional heterojunction is fabricated and characterized. This heterojunction comprises a Ni nanowire, a multiwalled carbon nanotube (MWCNT), and an amorphous carbon nanotube (a-CNT). The three components are in an end-to-end configuration, and form two MWCNT contacts, namely a Ni/MWCNT and an MWCNT/a-CNT contact. The interfacial structures of the two contacts show that multiple outer walls in the MWCNT simultaneously contact the Ni nanowire and the a-CNT, and can simultaneously participate in electrical transport. By investigating the electrical-transport properties of the heterojunctions, the two contacts to the MWCNT in every heterojunction are found to behave as two diodes connected in series face-to-face, at least one of which exhibits the characteristics of a nearly ideal Schottky diode and obeys thermionic-emission theory, wherein only the image force lowers the Schottky barrier. The appearance of this type of nearly ideal diode is attributed to the good contacts to the multiple outer walls of the MWCNTs realized by the heterojunctions' structures.