Robust coherent phonon mode at GaP/Si(001) heterointerface

Area of Science:

• Materials Science
• Solid State Physics
• Optoelectronics

Background:

• Lattice-matched Gallium Phosphide (GaP) layers on Silicon (Si) are crucial for optoelectronic devices.
• Defect-free GaP growth on Si(001) is achieved via a two-step process: low-temperature nucleation and high-temperature overgrowth.
• Previous studies identified a 2-THz phonon mode in thin GaP nucleation layers.

Purpose of the Study:

• To investigate the impact of the two-step growth procedure on ultrafast carrier and phonon dynamics at the GaP/Si interface.
• To understand the nature and behavior of the 2-THz interfacial phonon mode during different growth stages.

Main Methods:

• Transient reflectivity experiments were used to probe carrier and phonon dynamics.
• Analysis focused on the influence of GaP layer thickness and growth conditions (nucleation vs. overgrowth).

Main Results:

• The discrete electronic state influencing carrier dynamics in thin layers is suppressed by high-temperature overgrowth.
• The 2-THz phonon mode persists with constant frequency, independent of GaP thickness.
• Phonon amplitude shows non-monotonic dependence on GaP thickness and altered polarization dependence after overgrowth.

Conclusions:

• The 2-THz interfacial phonon mode is stable during high-temperature overgrowth.
• Phonon amplitude is governed by coupling to interfacial electronic transitions and atomic-scale structural changes.
• Understanding these dynamics is key for optimizing GaP/Si heterostructures for electronic and optoelectronic applications.