Analysis of dislocation defects in compositionally step-graded α-(Al Ga_1- )₂O₃ layers

Area of Science:

• Materials Science
• Semiconductor Physics
• Crystal Growth

Background:

• Alpha-gallium oxide (α-Ga2O3) is an ultra-wide bandgap semiconductor with potential for power electronics.
• Heteroepitaxial growth of α-Ga2O3 on sapphire substrates leads to significant dislocation defects due to lattice mismatch.
• Reducing dislocation density is crucial for improving the performance of α-Ga2O3-based devices.

Purpose of the Study:

• To develop a method for reducing dislocation density in α-Ga2O3 films grown on sapphire.
• To investigate the effectiveness of compositionally step-graded α-(AlxGa1-x)2O3 layers in mitigating defects.
• To explore the impact of introducing α-Ga2O3 layers within the graded structure.

Main Methods:

• Fabrication of compositionally step-graded α-(AlxGa1-x)2O3 layers using mist Chemical Vapor Deposition (CVD).
• Utilizing c-plane sapphire substrates for heteroepitaxial growth.
• Transmission Electron Microscopy (TEM) for defect analysis.

Main Results:

• Initial α-(Al0.96Ga0.04)2O3 layers showed few dislocations, while subsequent α-(Al0.84Ga0.16)2O3 layers had numerous dislocations.
• Step-graded layers induced dislocation bending under strain, reducing dislocation density by approximately 50% in higher Ga-content layers.
• Inserting multiple α-Ga2O3 layers into the graded structure further reduced dislocation defects at interfaces.

Conclusions:

• Compositionally graded layers effectively bend dislocations, mitigating defect propagation in α-Ga2O3 films.
• The strain induced by compositional variations is key to reducing dislocation density.
• Further optimization of layer composition, thickness, and stacking is expected to yield even lower dislocation densities.