Determination of Donor Gradients Within Surface Barriers Formed on Dense Cd‐Doped Barium Titanates

Abstract

Surface barriers were formed on dense Gd‐doped barium titanates by a reduction‐reoxidation process. The distribution of donors within the partially reoxidized barriers was determined from capacitance measurements using blocking contacts and from resistance measurements using ohmic contacts. The incremental barrier capacitance behaved as a depletion‐layer capacitance when measured as a function of bias voltage. A donor gradient αc was determined from the capacitance‐voltage behavior of the depletion layers by using a linear‐graded model to describe the donor distribution through the depletion layers. A donor gradient ar was indirectly determined from resistance profiles of the surface barriers formed on the reduced titanates by a second reoxidation. The donor gradients ac and ar were in good agreement, with both gradients decreasing for the higher reoxidation temperatures and/or the longer times used in forming the barriers. This behavior is explained by assuming that the reoxidation process is diffusion‐controlled and by qualitatively relating the gradients to assumed oxygen profiles within the barriers.