Measurement of polarization charge and conduction-band offset at InxGa1-xN/GaN heterojunction interfaces

The spontaneous and piezoelectric polarization fields in group-III nitride semiconductors lead to the presence of large electrostatic sheet charge densities at nitride semiconductor heterojunction interfaces. Precise quantitative knowledge of these polarization-induced charge densities and of the band-edge discontinuities at nitride heterojunction interfaces is therefore essential in nitride semiconductor device design and analysis. We have used capacitance-voltage profiling to measure the conduction-band offset and polarization charge density at InxGa1-xN/GaN heterojunction interfaces with x=0.054 and x=0.09. We obtain conduction-band offsets DeltaE(C)=0.09+/-0.07 eV for x=0.054 and DeltaE(C)=0.22+/-0.05 eV for x=0.09, corresponding to an averaged conduction-to-valence-band offset ratio DeltaE(C):DeltaE(V) of 58:42. Our measurements yield polarization charge densities of (1.80+/-0.32)x10(12) e/cm(2) for x=0.054 and (4.38+/-0.36)x10(12) e/cm(2) for x=0.09. These values are smaller than those predicted by recent theoretical calculations, but in good agreement with values inferred from a number of optical experiments. (C) 2004 American Institute of Physics.