Analysis of hole-like traps in deep level transient spectroscopy spectra of AlGaN/GaN heterojunctions

When a hole-like trap appears in deep level transient spectroscopy spectra of devices with an AlGaN/GaN heterojunction, surface states at the top of the AlGaN layer are often incriminated. However, no deep investigation has proved that this anomalous signal is related to interface states. In this work, we made a full study of a hole-like signal which appears in spectra of AlGaN/GaN Schottky barrier diodes. The mechanism responsible for the formation of the peak is determined, a model is proposed and this is then applied to make our analysis. We show that two deep donor levels in the AlGaN layer are responsible for the formation of the hole-like signal and we have determined their activation energies and their concentrations. With the help of secondary ion mass spectrometry studies, the dominant trap was assigned to a nitrogen antisite defect, which is in accordance with the literature. The second trap was tentatively associated with gallium vacancy related defects. The mechanism responsible for the formation of the hole-like signal allows the loss of electrons in the channel of the diode to be understood, and the amplitude of the peak is a way to quantify the importance of this loss.