Final answer:
A free electron in the conduction band that does not undergo recombination continues to contribute to electrical current, but it may also increase the lattice temperature due to energy transfer during collisions. Continuous power input is necessary to sustain the current, except in superconductors.
Step-by-step explanation:
When recombination doesn't occur for a free electron in the conduction band, the electron continues to move within the material due to the effect of the electric field. These free-electron collisions transfer energy to the lattice atoms of the semiconductor, possibly increasing temperature and increasing the likelihood of thermal vibrations. The lack of recombination means that the electron can contribute to the electrical current. However, in order to sustain this current, a continuous power input is essential, except in superconductors, which can maintain a current without a continual supply of energy.
Free electrons in the conduction band can contribute to the conductivity of the material, especially when additional donor impurities create an impurity band, which raises the Fermi level closer to the conduction band. In semiconductors at room temperature, many impurity electrons are thermally excited into the conduction band, increasing the electric current. Nonetheless, the excess kinetic energy provided by the electric field to free electrons does not translate into increased speed, as it is dissipated as thermal energy to the lattice, a principle that is critical in devices like lightbulb filaments.