The prospects for Ettingshausen and Peltier cooling at low temperatures

It is shown that the ambipolar Ettingshausen effect might be employed in a semi-metal or an intrinsic semiconductor to obtain useful cooling. The material should preferably have an energy gap less than kT , high effective masses and mobilities for both electrons and holes and a low lattice thermal conductivity. It is more likely that the right combination of properties will be found at low temperatures rather than at room temperature. It is also possible that phonon drag effects could increase the cooling effect. For this to happen the requirements are the same, except that the lattice thermal conductivity need not be low. So far, materials which have the required properties have not been found but by extrapolating from known semiconductors and semi-metals it is estimated that 30 degC of cooling at 80° K might be obtained from purely electronic effects. Higher values are rather unlikely, unless phonon drag effects could be exploited. Peltier cooling at low temperatures is also discussed briefly.