Ultrafast photoconductivity of crystalline, polycrystalline, and nanocomposite ZnSe material systems for terahertz applications

Abstract

Ultrafast photoconductivity is studied for crystalline (bulk), polycrystalline (microstructure), and nanocomposite (nanostructure) ZnSe material systems. Spectral transmission analyses show a pronounced red-shift of the absorption edge for only the nanocomposite ZnSe (being comprised of 500 nm nanoparticles in a polymer host). Ultrafast transient analyses show respective 6 ns, 1.5 ns, and 95 ps charge-carrier lifetimes for the respective material systems. The results are interpreted with a diffusion-recombination model, showing distinct regimes for bulk diffusion and surface recombination. Nanocomposite ZnSe is shown to be particularly advantageous for terahertz applications seeking ultrafast photoconductivity with high dielectric breakdown strengths and ultrashort charge-carrier lifetimes.