Cooling of electrons in a silicon inversion layer

Low temperature cooling of two-dimensional electrons in silicon-metal-oxide semiconductor field effect transistors is studied experimentally and found to be more effective than expected from the bulk electron-phonon coupling in silicon. The extracted heat transfer rate to phonons depends cubically on electron temperature, suggesting that piezoelectric coupling, which is absent in bulk silicon, dominates over deformation potential. As a result, at 100 mK. electrons farther than similar to100 mum from the contacts are mostly cooled by phonons. Using long devices and low excitation voltage we measure electron resistivity down to similar to100 mK and find that some of the metallic curves turn insulating below similar to300 mK.