Formation of two-dimensional electron and hole gases in undoped Al_xGa_1-xAs/GaAs heterostructures

Two-dimensional electron or hole gases (2DEG or 2DHG) are confined at the same interface in an undoped heterostructure by an electric field generated by a top gate. The combination of ion-implanted ohmic regions, an undoped heterostructure with superlattice barriers, and a metal gate is used to fabricate structures by a conventional process without self-alignment. High-quality 2DEG and 2DHG with a carrier density up to 8×10¹¹ cm^-2 are formed with a small gate leakage current. Switching between 2DEG and 2DHG at the same heterointerface is achieved by changing the sign of the gate voltage.