Charge Carrier Mobility Measurements in Beta-Carotene Glass by Transient Photoconductivity

Abstract

Transport of holes through beta-carotene glass was studied using a transient photoconductivity technique. The mobility is measured to be 1.5×10⁻³ cm²/V sec at 21°C and 10⁴ V/cm. The motion of carriers can be represented by transit time T_r, which means the time necessary for a charge carrier to travel from the front electrode to the counter-electrode of the sample. The inverse transit time (T_r)⁻¹ is found to vary with temperature T in the form of exp (−ε₀⁄kT), with ε₀=0.22 eV, and to vary with electric field E in the form of exp (α_cE^1⁄2) with α_e=2×10⁻³ (m/V)^1⁄2. Dielectric constant ε of beta-carotene glass was measured to be ε=1×10⁻¹⁰ F/m at 1 KHz. Using the Poole-Frenkel theory, the coefficient of E^1⁄2 in exp (α_tE^1⁄2) is estimated to be α_t=1×10⁻³ (m/V)^1⁄2. The observed α_e agrees approximately with the value of estimated α_t. Therefore, it is concluded that the transport of charge carrier is mainly controlled by the Poole-Frenkel effect.