FIELD-EFFECT MEASUREMENTS OF CARRIER MOBILITIES IN TRANSPARENT CONDUCTING FILMS OF AMORPHOUS INDIUM OXIDE

We report measurements of carrier mobilities in thin transparent films of amorphous indium oxide using the field effect. The field-effect mo bilities (of order 10(-3) m2 V-1 s-1) are similar to those calculated from conductivity and Hall effect measurements. Their similarity sets an upper limit of order 3 x 10(16) m-2 to the density of surface-trapp ed charges. The mobilities are temperature independent, consistent wit h being determined by ionized donor scattering which is known to domin ate in these systems. We show that conduction can be turned on in a de vice prepared on the insulator side of the metal-insulator transition with mobilities near threshold about an order of magnitude smaller tha n those observed at higher carrier densities. The difference is attrib uted to reduced screening. Failure to invert the channel suggests a si gnificant density of traps in addition to the oxygen vacancy donors.