Electron emission properties of nitrogen-induced localized defects in InAsN/GaAs quantum dots

The electron-emission properties of nitrogen-induced (N-induced) localized defects in InAsN/GaAs quantum dots (QDs) are investigated in detail by capacitance-voltage (C-V) profiling and bias-dependent deep-level transient spectroscopy (DLTS). The incorporation of nitrogen (N) into InAs QDs is shown to produce localized defects near QDs and threading-dislocation-related defects in the top GaAs layer. The threading dislocation is associated with an electron-emission energy of approximately 0.648 eV and emission from the sample surface toward the QDs. The electronemission energy from the QDs associated with the localized defects increases from 0.19 to 0.36 eV, indicating that both types of defect near QDs have low electron emission energies. Therefore, the change in emission energy is attributable to the defects across the QD interface where a band offset exists. The C-V profile at 300 K shows extended carrier depletion near the QDs. As ac frequency increases, an electron-emission peak emerges at the QDs; this peak is followed by another prominent peak, suggesting that the localized defect that is responsible for this latter peak has an energy below the QD electron ground state. On the basis of a C-V profile simulation, this defect is located at the QD at the observed emission energy below the GaAs conduction band, 360 meV. A comparison with InAsN QD and strain relaxation InAs QD samples reveals that the localized defect arises from a nitrogen alloy fluctuation in the QD. The energy location of this defect reveals a possibility that incorporated N is associated with a particular mode.