Deep-Level Defects Induced Degradation of Negative Differential Resistance in GaN-Based Resonant Tunneling Diodes

The degradation of the negative differential resistance (NDR) of GaN-based resonant tunneling diodes (RTDs) is a primary factor that limits their development into terahertz light source devices. In this work, on the basis of experiments and first-principles calculations, we proposed that deep-level defects in epitaxial materials can significantly affect the NDR of GaN-based RTDs. According to a low-frequency noise test, we confirmed the existence of 0.21 and 0.54 eV deep-level defects at the active region tunneling interface. The first-principles study of defect calculation based on the mixed functional theory reveals that the two deep-level defects originate from the interstitial defect Ni and the defect pair VN-NGa of the GaN side in the tunneling interface, respectively. In addition, AFM and TEM results indicate that threading dislocations are not the main factor fueling NDR degradation in the prepared RTDs. Our work suggests that the elimination of deep-level defects is the key to obtaining steady and reliable NDR in GaN-based RTDs.