Photoexcited carrier dynamics of thin film Cd3As2 grown on a GaAs(111)B substrate by molecular beam epitaxy

Abstract

The topological Dirac semimetal ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$ has drawn great attention for its novel physics and technical applications in optoelectronic devices operating in the infrared and THz regimes. Exploring the photoexcited carrier dynamics in ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$ is helpful to understand the transient carrier occupation and cooling processes that are closely associated with its unconventional band characteristic. Here, the photoexcited carrier dynamics in the ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$ thin film epitaxially grown on the $\mathrm{GaAs}(111)B$ substrate was investigated by employing the time-resolved midinfrared transient reflectance measurements, along with a theoretical modeling concerning the electron-polar optical ($e$-PO) phonon interaction. The measured photoexcited electron relaxation time of ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$ increases with the probe wavelength, and increases with temperature at temperatures higher than 30 K. Theoretical modeling under the framework of the two-temperature model can give qualitatively good description on both the temperature and probe wavelength dependence of the carrier relaxation time. Additionally, theoretical modeling shows that charge screening of the interaction of electrons with polar optical phonons can greatly reduce the hot carrier relaxation rate. The measured transient reflectance analyses indicate that the hot phonon effect plays a negligible role on the carrier relaxation in ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$. Our findings provide further insight into the photoexcited carrier dynamics in ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$ and valuable reference for developing its high-performance infrared optoelectronic devices.