Method for producing a hetero-bipolar transistor and hetero-bipolar-transistor

Method for the production of a hetero-bipolar transistor having an emitter composed of several layers in a mesa structure, and a ledge that projects laterally beyond the mesa structure, in a first emitter layer deposited on a base layer, composed of a layer sequence of semiconductor layers deposited over an entire area, and at least one cover layer, which serves, in structured manner, as a first mask for producing the emitter mesa structure, with under-etching of the cover layer, using material-selective etching processes, whereby the first emitter layer is covered by a stop layer that can be etched relative to the former, characterized in that after etching of the mesa structure up to the first stop layer, a passivation layer is deposited over the entire area, that the passivation layer is structured using a second mask, and that the ledge is etched with the passivation layer as a third mask, by means of an isotropic etching method, down to the base layer.