Sub-picosecond acoustic pulses at buried GaP/Si interfaces

TL;DR

This paper demonstrates the generation and detection of sub-picosecond acoustic pulses at GaP/Si interfaces using optical pump-probe techniques, revealing interface quality with nanometer-scale resolution.

Contribution

It introduces a method for ultrafast, non-destructive evaluation of buried semiconductor interfaces with sub-atomic spatial resolution.

Findings

Acoustic pulses with 0.5 ps width detected at interfaces.

Brillouin oscillations observed during pulse propagation.

Potential for nondestructive interface quality assessment.

Abstract

We report on the optical generation and detection of ultrashort acoustic pulses that propagate in three-dimensional semiconductor crystals. Photoexcitaiton of lattice-matched GaP layers grown on Si(001) gives rise to a sharp spike in transient reflectivity due to the acoustic pulse generated at the GaP/Si interface and detected at the GaP surface and vice versa. The extremely short width of the reflectivity spike, 0.5 ps, would translate to a spatial extent of 3 nm or 10 atomic bilayers, which is comparable with the width of the intermixing layer at the GaP/Si interface. The reflectivity signals are also modified by quasi-periodic Brillouin oscillations of GaP and Si arising from the acoustic pulses during the propagation in the crystals. The present results demonstrate the potential application of the simple optical pump-probe scheme in the nondestructive evaluation of the buried semiconductor interface quality.