Researchers demonstrate MoS2/AZO transparent rectifier

December 05, 2017 // By Julien Happich
Aiming to push 2D semiconductors nearer to commercialization, a team of researchers from King Abdullah University of Science & Technology (KAUST) have exploited a novel scalable CVD-based MoS2 deposition process together with the atomic layer deposition of transparent contacts to yield fully transparent ultra-thin and conformable transistors and inverters.

While monolayer MoS 2 is known to be transparent, the researchers investigated the use of transparent and aluminium doped zinc oxide (AZO) contacts whose composition they tuned through atomic layer deposition to achieve optimal conductivity and band-offsets with the MoS 2 layer.

Structure of the transparent thin film transistor.

In their paper "Large-Area Chemical Vapor Deposited MoS 2 with Transparent Conducting Oxide Contacts toward Fully Transparent 2D Electronics" published in the journal of Advanced Functional Materials, the researchers report fully transparent TCO/MoS 2 2D electronics with an average visible-range transmittance of 85% (92% for the MoS 2 monolayer and 85% for the whole stack).

A fully transparent field-effect rectifier (top) and a
NMOS inverter (bottom).

Patterning the MoS 2 films by plasma etching, they fabricated various transparent devices and circuits, including thin film transistors and a rectifier (a NMOS inverter) where the transparent oxide layers including 165nm-thin AZO contacts used for both the source/drain and gate electrodes, and a 55nm HfO 2 transparent gate dielectric were subsequently deposited by atomic layer deposition.

The transistors exhibited a high mobility of 4.2 cm 2 V −1 s −1, fast switching speed, a very low threshold voltage (0.69V) and a large switching ratio (4×10 8). Values that the authors claim to be record-breaking for monolayer CVD-processed MoS 2 transistors. The transparent fast switching inverters exhibited a gain of 155 at a supply voltage of 10V.

Next, the researchers aim to prove that their fabrication method is scalable to larger and more complex circuits, to open the path for a wider adoption of 2D semiconductors combined with transparent conducting oxides. Applications could include the fabrication of completely translucent components for transparent displays, smart windows and other concealed circuits

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