Influence of the electron blocking layer on defect state density and ultraviolet luminescence performance of the p-NiO/i-Ga2O3/n-GaN heterojunction

Abstract

Improving the efficiency of GaN-based light-emitting diodes (LEDs) had been a lifelong goal for researchers, with optimizing interfacial defects being a critical aspect of this pursuit. Here, optoelectronic devices (p-NiO/i-Ga₂O₃/n-GaN) with different thicknesses of i-Ga₂O₃ as electron blocking layers (EBLs) (sputtering times of 10, 30 and 60 min, respectively) were successfully fabricated for diodes A, B and C, respectively. Analysis revealed that diode B exhibited the most impressive performances, featuring the lowest series resistance (R_S) and defect state density of 24.46 Ω and 2.19×10¹⁰ cm^-3, respectively. The cross-sectional analysis of the Ga₂O₃ thin films provided a visual representation of the defect sources within the devices. As sputtering time increased, the Ga₂O₃ films underwent a cyclical pattern of structural changes, characterized by initial delamination, subsequent densification, and ultimately, a reoccurrence of delamination. Subsequently, the electroluminescence (EL) testing revealed that diode B outperformed diode A significantly, showing an ultraviolet (UV) luminescence intensity that was up to 15 times greater at equivalent injection currents. Based on these findings, we conducted variable temperature current-voltage (I-V) and EL tests on diode B to re-evaluate its performance. As anticipated, the results were encouraging, particularly in terms of the device’s exceptional activation energy of only 0.017 eV and stability.