Lampert triangle formation and relaxation behavior in doped poly(3,4-ethylenedioxythiophene) devices

Abstract

The current density–voltage (J–V) characteristics in stainless steel/poly(3,4-ethylenedioxythiophene)/Ag devices show the formation of the complete Lampert triangle (ΔABC) bounded by three limiting curves: Ohmic, trap-limited/filling space charge limited conduction, and trap-free/trap-filled space charge limited conduction. From the analysis of the Lampert triangle, values for carrier density (p0) ∼ 0.72 × 1013/cm3, mobility (μp) ∼ 77.47 × 10−4 cm2/V s, and transit time (tt) ∼ 10−12 s are obtained and also the transition voltages for different conduction mechanisms are estimated. The relaxation processes in bulk and interface are observed to be different from temperature-dependent impedance measurements. Estimated values of relaxation times are interface (τ1) ∼ 10−3 s and bulk (τ2) ∼ 10−6 s. Two parallel RQ (Q: constant phase element) circuits in series are used to fit the impedance data; however, the model varies for data at 110 and 120 K (two parallel CQ circuits in series). Since the samples have doped carriers, the activation energies are low (< 70 meV), and relaxation times follow Arrhenius behavior.