Ann‐p‐nheterojunction structure, formed by the epitaxial growth ofn‐Ge on ap‐GaAs substrate having a diffusedn‐GaAs region on the opposite face, has been employed to convert 1.5‐&mgr; radiation incident on then‐Ge face to 0.9‐&mgr; radiation emitted from then‐GaAs face. The internal quantum efficiency of then‐Ge,p‐GaAs heterojunction is 0.62; the spectral response of the heterojunction is typical of photon effects in Ge. The internal wavelength conversion efficiency is 2.8×10−5, limited principally by the low electroluminescent quantum efficiency of the GaAsp‐njunction at low injection current densities.