Novel Material for an Efficient Photodetector

In the last twenty years, metal-organic frameworks (MOFs) have become a coveted material system. So far, these highly porous substances, up to 90 percent of which are composed of empty space, have largely been used to store gases, for cata­lysis or to slowly release drugs in the human body. “The metal-organic framework compound developed at TU Dresden comprises an organic material integrated with iron ions,” explains Artur Erbe, head of the Transport in Nano­structures group at HZDR’s Institute of Ion Beam Physics and Materials Research. “The special thing about it is that the framework forms super­imposed layers with semi­conducting properties, which makes it poten­tially interesting for opto­electronic appli­cations.” The group had the idea of using the new semi­conducting two-dimensional MOF as a photo­detector.

Illustration of a photodetector, which is completely based on layers of metal-organic frameworks. Since this compound can detect and transform a broad range of light wavelengths into electrical signals, it could become a novel detector material. (Source: Juniks, HZDR)

In order to pursue it further, Himani Arora inves­tigated the semi­conductor’s electronic properties. She explored, among others, to what extent the light sensitivity was dependent on temperature and wavelength – and came to a promising con­clusion: From 400 to 1575 nanometers, the semi­conductor could detect a broad range of light wavelengths. The spectrum of radiation thus goes from ultra­violet to near infrared. “This is the first time we have proved such a broadband photo­detection for a photo­detector completely based on MOF layers,” the doctoral candidate notes. “These are ideal properties for using the material as an active element in opto­electronic components.”

The spectrum of wavelengths a semiconducting material can cover and transform into electrical signals essen­tially depends on the bandgap. The smaller the bandgap, the lesser the energy required to excite an electron. “As the bandgap in the material we explored is very small, only very little light energy is required to induce the elec­tricity,” Himani Arora explains. “This is the reason for the large range of the detectable spectrum.” By cooling the detector down to lower tempera­tures, the performance can be improved yet further because the thermal exci­tation of the electrons is supressed. Other improve­ments include opti­mizing the component configuration, producing more reliable contacts and developing the material further. The results suggest that the MOF-based photo­detectors will have a bright future. Thanks to their electronic pro­perties and inex­pensive manu­facturing, MOF layers are promising candidates for a raft of opto­electronic appli­cations.

“The next step is to scale the layer thickness,” says Artur Erbe, looking forward. “In the study, 1.7 micrometer MOF films were used to build the photo­detector. To integrate them into components, they need to be signi­ficantly thinner.” If possible, the aim is to reduce the super­imposed layers to 70 nanometers, that is, 25 times smaller than their size. Down to this layer thickness the material should exhibit comparable properties. If the group can prove that the func­tionality remains the same in these signi­ficantly thinner layers, they can then embark on developing it to the production stage. (Source: HZDR)

Reference: H. Arora et al.: Demonstration of a Broadband Photodetector Based on a Two‐Dimensional Metal–Organic Framework, Adv. Mat. 32, 1907063 (2020); DOI: 10.1002/adma.201907063

Link: Transport Phenomena in Nanostructures, Institute of Ion Beam Physics and Materials Research, Helmholtz‐Zentrum Dresden‐Rossendorf, Dresden, Germany

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