Nav: Home

New diode features optically controlled capacitance

June 06, 2017

WASHINGTON, D.C., June 6, 2017 -- A team of researchers at the Israel Institute of Technology has developed a new capacitor with a metal-insulator-semiconductor (MIS) diode structure that is tunable by illumination. The capacitor, which features embedded metal nanoparticles, is similar to a metal-insulator-metal (MIM) diode, except that the capacitance of the new device depends on illumination and exhibits a strong frequency dispersion, allowing for a high degree of tunability.

This new capacitor has the potential to enhance wireless capability for information processing, sensing and telecommunications. The researchers report their findings this week in the Journal of Applied Physics, from AIP Publishing.

"We have developed a capacitor with the unique ability to tune the capacitance by large amounts using light. Such changes are not possible in any other device," said Gadi Eisenstein, professor and director of the Russell Berrie Nanotechnology Institute at the Technion Israel Institute of Technology in Haifa and a co-author of the paper. "The observed photo sensitivity of this MIS diode structure expands its potential in optoelectronic circuits that can be used as a light-sensitive variable capacitor in remote sensing circuits."

MIM diodes are common elements in electronic devices, especially those utilizing radio frequency circuits. They comprise thin-film metal plate electrodes that are separated by an insulator. Like the MIM structure, the researchers' new MIS capacitor is bias independent, meaning the constant capacitance is independent of its supply voltage. Bias-independent capacitors are important for high linearity, and therefore straightforward predictability, of circuit performance.

"We have demonstrated that our MIS structure is superior to a standard MIM diode," said Vissarion (Beso) Mikhelashvili, senior research fellow at the Israel Institute of Technology and also a co-author of the paper. "On one hand, it has all the features of an MIM device, but the voltage independent capacitance is tunable by light, which means that the tuning functionality can be incorporated in photonic circuits."

"The illumination causes a twofold effect," Eisenstein said. "First, the excitation of trap states enhances the internal polarization. Second, it increases the minority carrier density (due to photo generation) and reduces the depletion region width. This change modifies the capacitance."

The researchers created three MIS structures, fabricated on a bulk silicon substrate, based on a multilayer dielectric stack, which consisted of a thin thermal silicon dioxide film and a hafnium oxide layer. The two layers were separated by strontium fluoride (SrF2) sublayers in which ferrum (Fe, iron) or cobalt (Co) nanoparticles were embedded.

The researchers found that the fluoridation-oxidation process of the iron atoms causes the formation of a gradient in the valence state of iron ions across the active layer, which results in the generation of an electronic polarization. The polarization causes a bias-independent depletion region and hence an MIM-type characteristic.

Four additional structures were prepared for comparison: Two lacked the SrF2 sublayers and one of them was prepared without the iron film. The other two structures contained SrF2: One did not have cobalt and the second included a one-nanometer Co layer.

The comparison with other MIS capacitors that contained the metal nanoparticles with or without the SrF2 sublayers led to the unequivocal conclusion that only devices consisting of the combination of Fe and SrF2 turn the MIS structure into a photo-sensitive MIM-like structure.
The article, "Optical control of capacitance in a metal-insulator-semiconductor diode with embedded metal nanoparticles," is authored by V. Mikhelashvili, G. Ankonina, Y. Kauffmann, G. Atiya, WD Kaplan, R. Padmanabhan and G. Eisenstein. The article will appear in the Journal of Applied Physics June 6, 2017 [DOI: 10.1063/1.4983760]. After that date, it can be accessed at


Journal of Applied Physics is an influential international journal publishing significant new experimental and theoretical results of applied physics research. See

American Institute of Physics

Related Nanoparticles Articles:

Chemists perform surgery on nanoparticles
A team of chemists led by Carnegie Mellon's Rongchao Jin has for the first time conducted site-specific surgery on a nanoparticle.
Nanoparticles remain unpredictable
The way that nanoparticles behave in the environment is extremely complex.
Gold standards for nanoparticles
KAUST researchers reveal how small organic 'citrate' ions can stabilize gold nanoparticles, assisting research on the structures' potential.
Lipid nanoparticles for gene therapy
Twenty-five years have passed since the publication of the first work on solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) as a system for delivering drugs.
Nanoparticles hitchhiking their way along strands of hair
In shampoo ads, hair always looks like a shiny, smooth surface.
Better contrast agents based on nanoparticles
Scientists at the University of Basel have developed nanoparticles which can serve as efficient contrast agents for magnetic resonance imaging.
Gentle cancer treatment using nanoparticles works
Cancer treatments based on laser irridation of tiny nanoparticles that are injected directly into the cancer tumor are working and can destroy the cancer from within.
Radiation-guided nanoparticles zero in on metastatic cancer
Zap a tumor with radiation to trigger expression of a molecule, then attack that molecule with a drug-loaded nanoparticle.
Nanoparticles can grow in cubic shape
Use of nanoparticles in many applications, e.g. for catalysis, relies on the surface area of the particles.
Nanoparticles deliver anticancer cluster bombs
Scientists have devised a triple-stage 'cluster bomb' system for delivering the chemotherapy drug cisplatin, via tiny nanoparticles designed to break up when they reach a tumor.

Related Nanoparticles Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#532 A Class Conversation
This week we take a look at the sociology of class. What factors create and impact class? How do we try and study it? How does class play out differently in different countries like the US and the UK? How does it impact the political system? We talk with Daniel Laurison, Assistant Professor of Sociology at Swarthmore College and coauthor of the book "The Class Ceiling: Why it Pays to be Privileged", about class and its impacts on people and our systems.