Carrier Lifetimes in a GaPAsN Intermediate Band Semiconductor

Multiband semiconductors may form the basis of efficient intermediate band solar cells, if sufficiently long carrier lifetimes can be engineered. We used transient absorption spectroscopy to measure carrier lifetimes in GaP$_{\mathrm{y}}$As$_{\mathrm{1-x-y}}$N$_{\mathrm{x}}$. These measurements probe carrier populations in the conduction band, intermediate band and valance band as a function of time after an excitation pulse. ~ Following photoexcitation of GaP$_{\mathrm{0.32}}$As$_{\mathrm{0.67}}$N$_{\mathrm{0.01\thinspace }}$we find that the electron population in the conduction band decays exponentially with a time constant $t_{\mathrm{CB}} \quad =$23ps. Electrons in the intermediate band exhibit bimolecular recombination with holes with recombination constant $r \quad =$ 2\textbullet 10$^{\mathrm{-8}}$ cm$^{\mathrm{-3}}$/s. An optical pump pulse excited electrons from the valance band to the intermediate and conduction bands, and the change in interband absorption was probed with a delayed white light pulse. We modeled the optical properties of our samples using the band anti-crossing model to extract carrier densities as a function of time. We will also report THz Transient photoconductivity measurements in these materials.