Effect of strain-induced defects in GaN channel on two-dimensional carrier transport in AlGaN/GaN heterostructures

To improve the mobility of two-dimensional electron gas (2DEG) in an AlGaN/GaN heterostructure grown by metalorganic chemical vapor deposition, we characterized the defect distribution around the interface with and without an AlN interlayer by the steady-state photocapacitance method under controlling the bias voltage and incident photon energy. For samples without the AlN interlayer, the defects in the GaN channel layer near the heterointerface were induced by the strain from the Al1−xGaxN barrier depending on the AlN mol fraction. The density of strain-induced defects was markedly increased near the conduction band minimum to 1 × 1018 cm−3 peaked at a depth of ∼10 nm from the heterointerface for the Al0.24Ga0.76N/GaN sample. The AlN interlayer was confirmed to suppress the formation of strain-induced defects. The carrier mobility evaluated by magneto transport measurements was also improved clearly in samples with the AlN layer because of the reduction in the density of strain-induced defects leading to remote 2DEG scattering. We have clarified the correlation between the density of strain-induced defects and the 2DEG mobility for a comprehensive understanding of the carrier transport in strained heterostructures.