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 ${\mathrm{In}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N/GaN}$ heterojunction interfaces with $\text{x=0.054}$ and $\text{x=0.09.}$ We obtain conduction-band offsets ${\mathrm{\Delta E}}_C\text{=0.09±0.07\hspace{0.17em}}\mathrm{eV}$ for $\text{x=0.054}$ and ${\mathrm{\Delta E}}_C\text{=0.22±0.05\hspace{0.17em}}\mathrm{eV}$ for $\text{x=0.09,}$ corresponding to an averaged conduction-to-valence-band offset ratio ${\mathrm{\Delta E}}_C{\mathrm{:\Delta E}}_V$ of 58:42. Our measurements yield polarization charge densities of ${\text{(1.80±0.32)×10}}^{12}\hspace{0.17em}{\mathrm{e/cm}}^2$ for $\text{x=0.054}$ and ${\text{(4.38±0.36)×10}}^{12}\mathrm{\hspace{0.17em}e/}{\mathrm{cm}}^2$ for $\text{x=0.09.}$ These values are smaller than those predicted by recent theoretical calculations, but in good agreement with values inferred from a number of optical experiments.