Thin perfect absorbers on top of CMOS

Leuven - PhD
More than two weeks ago

Classical imager materials have very long absorption lengths, which hamper pixel downscaling. Recent progress shows that new metamaterials can be constructed with very short absorption lengths for future high-resolution imager applications.


Classical imagers for visible light use silicon as the absorbing semiconductor. But the absorption length in silicon for the visible is rather long, e.g. more than 6 microns for red light. The pixel dimensions of advance imagers are much smaller, going down to even 0.7 microns. As a consequence, it is a huge technological challenge to avoid crosstalk in those structures.

However, recent work [1-4] indicates that new meta-materials can be engineered such that perfect absorption can be obtained in layers of only a few nanometers thick. It is clear that such stacks, when integrated in an imager stack on top of CMOS can avoid the crosstalk problems and enable further downscaling of CMOS imagers.

This PhD topic focusses on the engineering and the experimental verification of those stacks for use on top of CMOS.


Applications are obviously broader than only imagers. Also, amongst others photovoltaics can benefit from these metamaterial stacks.



[1] A. Ghobadi, et al.,, “Strong Light–Matter Interaction in Lithography-Free Planar Metamaterial Perfect Absorbers,” ACS Photonics 5, p. 4203, Nov. 2018.

[2] M.R.S. Dias, et al., “Lithography-Free, Omnidirectional, CMOS-Compatible AlCu Alloys for Thin-Film Superabsorbers,” Advanced Optical Materials 6, p. 1700830, Jan. 2018.

[3] J. Rensberg et al., “Epsilon-Near-Zero Substrate Engineering for Ultrathin-Film Perfect Absorbers,” Phys. Rev. Applied  8, p. 014009, Jul. 2017.

[4 ]V. Steenhoff, et al., “Ultrathin Resonant-Cavity-Enhanced Solar Cells with Amorphous Germanium Absorbers,” Advanced Optical Materials 3, p 182, 2015.

Required background: Engineering Science, Physics, Engineering Technology

Type of work: 20% literature, 30% modeling, 50% experimental characterisation

Supervisor: Jan Genoe

Daily advisor: Robert Gehlhaar

The reference code for this position is 2020-091. Mention this reference code on your application form.


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