Localized or Delocalized Electrons in Microcrystalline Silicon?

Abstract

ABSTRACTThe temperature dependence (4.2 - 300 K) of the electron spin resonance (ESR) signal at g = 1.998 and the electronic conductivity in microcrystalline silicon are measured and related with each other for a series of n-type samples. In addition the hyperfine interaction with the phosphorus donor states is investigated. The conductivity at low temperatures can be interpreted as hopping in impurity states with activation energies of a few meV very similar to n-doped crystalline silicon. The ESR intensity follows a 1/T-Curie law dependence. The carrier densities determined from the dopant concentration, electrical transport and ESR, respectively, agree surprisingly well. Little hyperfine intensity is found which is explained by exchange interaction of electrons with more than one dopant nucleus or occupation of tail states at low doping levels. It is concluded that the excess carriers introduced through doping do for their major part contribute to both transport and ESR. The results are in accordance with a position of the electrons with g=1.998 in impurity or tail states of the crystalline grains at low temperatures. With increasing temperature carriers get excited into the conduction band - a transition which is also monitored in the conductivity - where the ESR line is subject to considerable line broadening.