The "Meyer-Neldel" Rule: Investigation and Application on Semiconductors

Abstract

Simple chemical bath deposition technique is successfully used to prepare nc-PbSe films with an average grain size of 21±6 nm for 54.5:45.5 Pb/Se ratios (Bohr exciton radius of PbSe= 46 nm).  The prepared small-granule size of PbSe relative to its large Bohr exciton radius leads to a quantum confinement that led to an increase in the optical band gap to 1.12±0.01 eV gap; i.e., three times larger than that of the bulk (EgBulk = 0.28 eV).  The temperature dependence of dark dc conductivity (77–350 K) for nc-PbSe films showed an Arrhenius behavior similar to that of the non- crystalline semiconductors with a monotonic linear decrease character within the thermal annealing time sequence.  The dominant conduction mechanism is thermoionic emission from 285 K to 350 K, and thermally assisted tunneling below that range.  The observed good correlation between σo and ΔE with a positive EMN value indicates there is an evidence for the validity of MNR in nc-PbSe under the effect of annealing, light exposure, ac frequency change, and γ-irradiation.  The positive character of EMN (EMN>0) for nc-PbSe is similar to that found in different forms of non-crystalline chalcogenide semiconductors (amorphous films, liquids and bulk glasses).  The values of Meyer-Neldel energy EMN for all dark dc conductivity investigated samples are in the range (20 meV - 60 meV) reported by SAW (Shimakawa & Abdel-Wahab, 1997), while EMN for light exposed dc conductivity is smaller, and is larger for ac conductivity, the reason of this observation needs further studies.