Polarization charges and polarization-induced barriers in AlxGa1-xN/GaN and InyGa1-yN/GaN heterostructures

Polarization charges are measured and the formation of large electrostatic barriers arising primarily as a consequence of the presence of polarization -induced charge densities is deduced from capacitance-voltage analysis of n -type AlxGa1-xN/GaN and InyGa1-yN/GaN heterostructures. In structures consi sting of 5-10 nm AlxGa1-xN or InyGa1-yN surrounded by n-GaN, capacitance-vo ltage profiling studies combined with elementary electrostatic analysis yie ld experimental estimates of polarization charge densities, which are compa red with values expected based on the combined effects of spontaneous and p iezoelectric polarization. These results imply the existence of electrostat ic barriers that are due primarily to the large polarization charge densiti es at each heterojunction interface and the resulting potential difference maintained across the thin AlxGa1-xN or InyGa1-yN layers. The electrostatic barriers formed in these structures are large in comparison to the heteroj unction conduction-band offsets, demonstrating the utility of polarization- based engineering of electrostatic barriers in nitride semiconductor hetero structures. (C) 2001 American Institute of Physics.