Integrated assemblies containing germanium

An integrated circuit assembly, comprising:

• a first semiconductor structure comprising heavily-doped silicon;
• a germanium-containing interface material over the first semiconductor structure, the germanium-containing interface material consisting of a material selected from non-oxidized germanium and partially oxidized germanium;
• a protective material comprising one or both of Si and Ge over the germanium-containing interface material;
• an opening extending entirely through the protective material;
• and
• a second semiconductor structure extending within the opening and contacting the germanium-containing interface material;
• the second semiconductor structure having a heavily-doped lower region adjacent the germanium-containing interface material and having a lightly-doped upper region above the heavily-doped lower region;
• the lightly-doped upper region and heavily-doped lower region being majority doped to a same dopant type, and joining to one another along a boundary region.