Heterojunction bipolar transistors are provided that include at least one contact (e.g., collector, emitter, and/or base) formed by a heterojunction between a crystalline semiconductor material and a doped non-crystalline semiconductor material layer. An interfacial intrinsic non-crystalline semiconductor material layer is present at the heterojunction between the crystalline semiconductor material and the doped non-crystalline semiconductor material layer. The presence of the interfacial intrinsic non-crystalline semiconductor material layer improves the surface passivation of the crystalline semiconductor material by reducing the interface defect density at the heterojunction.