Selective substitution induced anomalous phonon stiffening within quasi-one-dimensional P-P chains in SiP2

Light-matter interactions in low-dimensional quantum-confined structures can dominate the optical properties of the materials and lead to optoelectronic applications. In anisotropic layered silicon diphosphide (SiP2) crystal, the embedded quasi-one-dimensional (1D) phosphorus-phosphorus (P-P) chains directly result in an unconventional quasi-1D excitonic state, and a special phonon mode vibrating along the P-P chains, establishing a unique 1D quantum-confined system. Alloying SiP2 with the homologous element serves as an effective way to study the properties of these excitons and phonons associated with the quasi-1D P-P chains, as well as the strong interaction between these quasi-particles. However, the experimental observation and the related optical spectral understanding of SiP2 with isoelectronic dopants remain elusive. Herein, with the photoluminescence and Raman spectroscopy measurements, we demonstrate the redshift of the confined excitonic peak and the stiffening of the phonon vibration mode B-1g(3) of a series of Si(P1-xAsx)(2) alloys with increasing arsenic (As) compositions. This anomalous stiffening of is attributed to the selective substitution of As atoms for P atoms within the P-P chains, which is confirmed via our scanning transmission electron microscopy investigation. Such optical spectra evolutions with selective substitution pave a new way to understand the 1D quantum confinement in semiconductors, offering opportunities to explore quasi-1D characteristics in SiP2 and the resulting photonic device application.

Automated summary

The interaction between light and matter in low-dimensional quantum-confined structures can greatly influence the optical properties of materials and have applications in optoelectronics. In the anisotropic layered silicon diphosphide (SiP2) crystal, the quasi-one-dimensional (1D) phosphorus-phosphorus (P-P) chains create an unconventional quasi-1D excitonic state and a unique 1D quantum-confined system. By alloying SiP2 with a similar element, researchers can study the properties of these excitons and phonons associated with the quasi-1D P-P chains, as well as their strong interaction. However, the experimental observation and understanding of SiP2 with isoelectronic dopants is still unclear. In this study, the authors use photoluminescence and Raman spectroscopy measurements to observe the redshift of the confined excitonic peak and the stiffening of the phonon vibration mode in Si(P1-xAsx)2 alloys with increasing arsenic (As) compositions. This anomalous stiffening is attributed to the selective substitution of As atoms for P atoms within the P-P chains, as confirmed by scanning transmission electron microscopy. These optical spectrum changes provide insights into 1D quantum confinement in semiconductors and offer opportunities for photonic device applications.