Stacking faults in ß-Ga2O3 crystals observed by X-ray topography.

Planar defects in -oriented ß-Ga2O3 wafers were studied using X-ray topography. These planar defects were rectangular with dimensions of 50-150 µm, and the X-ray topography analysis revealed that they were stacking faults (SFs) enclosed by a single partial dislocation loop on the plane. The SF formation was found to be supported by a unique structural feature of the plane as a slip plane; the plane consists of close-packed octahedral Ga and O layers, allowing slips to form SFs. Vacancy arrays along the b axis in the octahedral Ga layer reduce the self-energy of the edge component in the partial dislocation extending along the b axis. It is speculated that the SFs occur during the crystal growth process for unknown reasons and then recover owing to elastic instability after initially increasing in size as crystal growth proceeds. Based on this analysis, a structural model for the SFs is proposed.

High-Efficiency InGaN/GaN Quantum Well-Based Vertical Light-Emitting Diodes Fabricated on ß-Ga2O3 Substrate.

We demonstrate a state-of-the-art high-efficiency GaN-based vertical light-emitting diode (VLED) grown on a transparent and conductive (-201)-oriented (ß-Ga2O3) substrate, obtained using a straightforward growth process that does not require a high-cost lift-off technique or complex fabrication process. The high-resolution scanning transmission electron microscopy (STEM) images confirm that we produced high quality upper layers, including a multiquantum well (MQW) grown on the masked ß-Ga2O3 substrate. STEM imaging also shows a well-defined MQW without InN diffusion into the barrier. Electroluminescence (EL) measurements at room temperature indicate that we achieved a very high internal quantum efficiency (IQE) of 78%; at lower temperatures, IQE reaches ∼86%. The photoluminescence (PL) and time-resolved PL analysis indicate that, at a high carrier injection density, the emission is dominated by radiative recombination with a negligible Auger effect; no quantum-confined Stark effect is observed. At low temperatures, no efficiency droop is observed at a high carrier injection density, indicating the superior VLED structure obtained without lift-off processing, which is cost-effective for large-scale devices.