The scattering of phonons by bound electrons in a semiconductor

In a fairly pure semiconductor at low temperatures, the carriers are in states bound to impurity atoms. In compensated material, there will be some bound states which are not occupied. A carrier can jump from one impurity state to an unoccupied neighbour, and thereby interact with lattice waves, setting up a thermal resistance. We calculate the effective mean free path of phonons affected by this mechanism. This mean free path varies inversely as the number of carriers and the number of vacancies, and as a function of temperature has a minimum, at about 0·2°K for ‘light’ holes in germa nium. Some phenomena in the thermal conductivity of gerinanium are thought to be due to this effect.