No abstract

Polycrystalline silicon is deposited by pyrolysis of silane in an rf heated epitaxial reactor. The grains exhibit a fibrous microstructure having an 〈110〉 preferred orientation in the growth direction. Growth is inhibited in the presence of excess arsine and accelerated in the presence of diborane. The results are explained in terms of catalysis and poisoning of surface adsorption sites responsible for reaction. A simple model for current conduction in polycrystalline silicon is described based on grain size, grain doping, and effective barrier height due to the grain boundary. This model satisfactorily explains the observed temperature dependence of the resistivity of undoped films and also the large values of resistivity which are observed for dopant concentrations ≲1015 cm−3 .

No abstract

A model of current transport in ZnO varistors is proposed. The model is a modification of an earlier one suggested by Levine, with the major difference being the inclusion of a thin (?10 Å) ’’disordered’’ layer which separates the single-crystal ZnO grains. The proposed model is shown to be consistent with electrical and microstructural observations and can satisfactorily account for α’s in excess of 60. A technique for extracting the surface-state density Ns(E) and doping profiles from C-V and I-V data is described. It is also shown from the theory that the maximum α is approximately proportional to the grain voltage, a result that is in agreement with measurements on varistors made under a wide range of processing conditions. By calculating the I-V characteristic for different Ns(E) profiles, it is shown that Ns(E) largely determines this characteristic and that certain profiles are to be favored over others when processing conditions are considered.

No abstract