  We have observed the Josephson effect in junctions formed between single
crystals of SrFe1.74Co0.26As2 and Ba0.23K0.77Fe2As2. I-V curves showed
resistively-shunted junction characteristics, and the ac Josephson effect was
observed under microwave irradiation. By applying an in-plane magnetic field,
the critical current is completely modulated and shows a relatively symmetric
diffraction pattern, consistent with the intermediate junction limit. The
observation of the Josephson effect in the p-n bicrystal structure not only has
significant implications for designing phase-sensitive junctions to probe the
pairing symmetry of iron pnictide superconductors, but also represents an
important step in developing all iron pnictide devices for applications.
