The Meyer–Neldel rule in hydrogenated amorphous silicon n i n devices

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Abstract
Conductivity measurements on hydrogenated amorphous silicon (a‐Si:H) nin devices with several i‐layer thicknesses are reported. The ohmic conductivity (σ) is found to follow the Meyer–Neldel rule (MNR): σ=σ00 exp(Ea/kT0) exp(−Ea/kT), where Ea is the conductivity activation energy, k is Boltzmann’s constant, and T is the temperature. It is shown that the MNR arises because of the form of the a‐Si:H gap state distribution that induces a statistical shift of the Fermi energy with the required functional form and magnitude. The characteristic temperature T0 is related to the slope G=1/kTc of the exponential conduction‐band tail state distribution according to kT0≂1.7kTc. The conductivity prefactor can be expressed as σ00=CNceμ, where Nc is the density of states (DOS) above the mobility edge, e is the electron charge, μ is the microscopic electronic mobility, and C is a constant of the order of 10−6 eV. Evaluation of the data gives σ00=10−2.9 (Ω cm)−1, and T0=570 K, i. e., Tc=340 K. This σ00 value corresponds to realistic values of Nc≂1021 cm−3 eV−1 and μ≂10 cm2/V s. DOS data are also deduced from the space‐charge‐limited conduction (SCLC) of the nin’s at higher voltages. In this way a consistent DOS distribution for the upper half of the a‐Si:H band gap is obtained. SCLC analysis indicates a minimum gap state density N0=4×1016 cm−3 eV−1. UFAIPXR