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Work function and AC operating gas‐sensitive films based on quaternary chalcogenides
Author(s) -
Tsiulyanu D.,
Ciobanu M.,
Liess H.D.
Publication year - 2016
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.201552500
Subject(s) - chalcogenide , band bending , amorphous solid , fermi level , work function , heterojunction , semiconductor , materials science , chemisorption , tellurium , analytical chemistry (journal) , condensed matter physics , chemistry , optoelectronics , electron , nanotechnology , adsorption , inorganic chemistry , crystallography , physics , organic chemistry , quantum mechanics , chromatography , layer (electronics)
A study of quaternary alloys of As–S–Ge–Te was performed in order to assess their use in future gas sensors operating at room temperature. To elucidate the effect of tellurium, the quaternary compositionsAs 2 Te 13Ge 8 S 3andAs 2 Te 130Ge 8 S 3 , with increasing concentration of Te have been considered along with pure tellurium films. SEM, AFM, and X‐ray analysis have shown that the nature of the films was predominantly amorphous. To overcome the sensing disadvantage of DC chalcogenide‐based sensors due to small signal/noise ratio, gas‐sensing measurements were performed using both potential difference (Kelvin probe) and AC methods. The work‐function measurements showed that the amorphous chalcogenides in question are suitable materials for the detection of small concentrations of NO 2 . The sensing mechanism of NO 2 is explained by “strong” chemisorptions via interaction of adsorbed species with lone‐pair electrons, which form the upper part of the valence band of chalcogenide semiconductors. The chemisorption of NO 2 molecules results in increases in both work‐function change Δ Φ > 0 and electrical conductivity Δ σ > 0 because of the additional charging of the surface and band bending. The impedance spectra, being strongly influenced by gaseous environment, depend on material composition and film microstructure. The frequency‐dependent impedance sensitivity to nitrogen dioxide denotes the competitive influence of carrier transport via states of allowed bands, hopping between localized states in the extended band tails and tunneling (variable‐range hopping) between localized states close to the Fermi level. Impedance sensitivity, being maximal for amorphousAs 2 Te 13Ge 8 S 3 , is assumed to be controlled by competition of these charge‐transport mechanisms.