Polarization charge densities at p-GaN/n-AlGaN heterojunctions evaluated by capacitance-voltage characteristics

We propose a new method to evaluate the polarization charge density induced at hetero-interfaces using capacitance-voltage characteristics of p-n heterojunctions and have applied this method to p-GaN/n-AlGaN heterojunction diodes. This method uses p-n heterojunction structures instead of undoped ones, so the obtained result is less influenced by background impurities or deep levels. Furthermore, it is possible to evaluate the negative polarization charge densities for GaN on top of AlGaN heterostructures. The experimental results indicate that the negative polarization charges with their densities more than 5 × 10¹² cm^-2 are induced at the GaN/AlGaN hetero-interfaces for the Al mole fractions above 11%.