A GaAs phononic crystal with shallow noncylindrical holes

Area of Science:

• Materials Science
• Acoustics
• Nanotechnology

Background:

• Phononic crystals (PnCs) are engineered structures that control the propagation of acoustic waves.
• Gallium arsenide (GaAs) is a semiconductor material with applications in electronics and photonics.
• Surface acoustic waves (SAWs) are mechanical waves that propagate along the surface of a solid.

Purpose of the Study:

• To investigate the phononic crystal properties of a square lattice of shallow holes in GaAs.
• To demonstrate the effectiveness of this structure as a phononic crystal reflector for surface acoustic waves.
• To analyze the impact of noncylindrical hole shapes on phononic crystal performance.

Main Methods:

• Fabrication of a GaAs substrate with a square lattice of shallow holes using photolithography and wet-etching (citric acid:H2O2).
• Characterization of the phononic crystal reflector using insertion loss measurements.
• Interferometric imaging of surface acoustic waves propagating on the GaAs surface.
• Comparison of experimental results with finite-difference time-domain (FDTD) simulations.

Main Results:

• The fabricated structure demonstrated phononic crystal behavior, acting as a reflector for surface acoustic waves.
• Despite limitations in hole depth and shape due to non-uniform etching, the phononic crystal effect was confirmed.
• Experimental measurements of surface phonon displacement showed good agreement with FDTD simulations of rounded-square holes.
• Insertion loss measurements confirmed the wave-reflecting properties of the phononic crystal.

Conclusions:

• A square lattice of shallow, noncylindrical holes in GaAs can function as an effective phononic crystal reflector.
• The study validates the use of wet-etching techniques for creating phononic crystal structures in GaAs.
• The findings suggest potential applications in controlling and manipulating surface acoustic waves in semiconductor devices.