Optimization of metal oxides for the realization of electrode in adequacy with the photosensitive material in the near infrared

Published : 8 October 2019

The thesis is part of a partnership between CEA-Léti and the Process Development Department of STMicroelectronics Crolles.

The study will focus on the development of electrodes for image sensor applications.

The next generations of image sensors will use chalcogenide, perovskite or ‘quantum dots’ photosensitive materials. These materials are inserted between electrodes to collect electrons and generated photo holes. Band engineering is necessary to promote the transfer of charges to the electrodes when the photosensitive material is illuminated, whereas when the detector is in the dark it is necessary to block the continuous flow of thermally activated charges through the structure, this flux may lead to a dark current level too high. The electrodes must also be stable in contact with these new materials, that is to say that it is necessary to limit the interface chemical reactions which can lead to the trapping of charges, or to an undesired shift of the levels of energy of the valence or conduction bands. The upper electrode must be deposited by a technique that does not degrade the photosensitive materials that are known to be fragile and easily degrade under an oxidizing atmosphere, under UV radiation or under bombardment during deposition using a plasma. Finally, these electrodes must be conductive, and the upper electrode must be transparent for the photons that pass through it.

The objective of the thesis is to develop and optimize a new upper electrode adapted to image sensors operating in the field of near IR (1-1.5µm)

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