Deep-level transient spectroscopy of defect states at <i>p</i>-type oxide/β-Ga2O3 heterojunctions

Defects in p-type oxide/β-Ga2O3 heterojunction diodes were investigated using p-type Cu2O as a case study. Diodes with polycrystalline and epitaxial Cu2O films were analyzed using deep-level transient spectroscopy. For both diodes, two electron bulk defects were detected, including a minority defect at 0.23 eV below EC within Cu2O and a majority defect at 0.53 eV below EC within β-Ga2O3. Furthermore, a high-density interface state of 4.5 × 1012 cm−2/eV was observed in the polycrystalline Cu2O/β-Ga2O3 diode. The presence of a high density of interface states helped reduce the turn-on voltage owing to the interface recombination current. However, it also enabled electron carriers to tunnel through the interface to β-Ga2O3, followed by variable range hopping through the bulk defect in the β-Ga2O3 layer, ultimately causing undesirable premature breakdown. The results of this study underscore the critical role of optimizing the crystal structure during p-type oxide growth for desired defect characteristics, particularly concerning interface states, in β-Ga2O3 bipolar devices for different applications, offering insights for high-performance power rectifier development.