Three-dimensional memory device containing heterojunction source layer and method for manufacturing the same

A method of forming a memory device, comprising:

• forming an alternating stack of insulating layers and spacer material layers over a carrier substrate, wherein the spacer material layers are formed as or are subsequently replaced with electrically conductive layers;
• forming a memory opening through the alternating stack;
• forming a memory opening fill structure in the memory opening, wherein the memory opening fill structure comprises a memory film and a vertical semiconductor channel comprising a first semiconductor material having a first band gap;
• removing the carrier substrate;
• forming a cavity within a volume of the memory opening and exposing a surface of the vertical semiconductor channel from a side of the memory opening from which the carrier substrate is removed;
• forming an interfacial source layer comprising a second semiconductor material having a second band gap that is different from the first band gap on an end portion of the vertical semiconductor channel at least in a first portion of the cavity;
• and
• forming a primary source layer comprising a third semiconductor material having a third band gap that is different from the second band gap on the interfacial source layer.