Sorption-induced conductivity changes in thin compound semiconductors

A Model for the Operation of a Thin‐Film SnO x Conductance‐Modulation Carbon Monoxide Sensor

“…From the standpoint of the semiconductivity of the sensor, the chemisorbed species Ahave replaced the shallow donors as the principal source of conduction band electrons in the detailed balance relations among the various electronic states that determine the location of the Fermi level of the sensor. More or less complete depletion of thin, insulating semiconductor specimens leads to a drastic reduction in the specimen conductance, as verified with CdS single crystals and thin films (13). The above mechanism is justified for the SnOz sensor by the similar observation of a drastic reduction in conductance on the exposure of a well out-gased sensor to oxygen.…”

“…In the present model, the sites SA(A) can be viewed as "holes" left behind by the transfer of charges from the SA sites to the conduction band by the incident flux of the reactant gas R. Thus, Eq [16] is equivalent to Eq. [13]. Further, for very insulating photoconductors, An _~ n and ap ___ p so that n~_p [17] which is equivalent to Eq.…”

“…These sites, in turn, have been converted rapidly, one-for-one, into SA(A) sites by the reactions [4c], [4d], and [3a]. Again, in terms of concentrations, this means that An : SA(A) [13] where ,~n is actually the incremental change in the conduction band electron concentration defined by n : no + An [14] where n is the total electron concentration and no is the background concentration in the absence of the reactant gas (see Eq. [19] below).…”