Electrochemical and photoelectrochemical deposition of thallium(III) oxide thin films

Thallium (III) oxide is a degenerate n-type semiconductor with high optical transparency and electrical conductivity. Films of thallium(III) oxide can be electrochemically deposited onto conducting and p-type semiconducting substrates, and photoelectrochemically deposited onto n-type semiconducting substrates. Films deposited at currents below the mass transport limit onto platinum or stainless steel were columnar, and the current efficiency on stainless steel was 103 ±2%. Dendritic films were deposited at mass-transport-limited currents. Films were deposited with thicknesses ranging from 0.1 μm on n-silicon, to 170 μm on stainless steel. The photoelectrochemically deposited films were “direct-written” onto n-silicon, since the material was deposited only at irradiated portions of the electrode. Thin films were grown by irradiating the n-silicon with 450 nm monochromatic light, since the light was strongly absorbed by the thallium(III) oxide. The most uniform thin films were deposited when the n-silicon was initially irradiated with a short pulse of high intensity light. The pulse apparently promoted instantaneous nucleation of a high density of thallium(III) oxide nuclei.