Nyt atomisk tyndt materiale kan forbedre effektiviteten af ​​lysbaseret teknologi

Solpaneler, kameraer, biosensorer og fiberoptik er teknologier, der er afhængige af fotodetektorer eller sensorer, der omdanner lys til elektricitet. Fotodetektorer bliver mere effektive og overkommelige, med deres komponenthalvlederchips aftagende i størrelse. Denne miniaturisering skubber dog imod grænser sat af nuværende materialer og fremstillingsmetoder, hvilket tvinger afvejninger mellem størrelse og ydeevne.

Der er mange begrænsninger ved den traditionelle halvlederchip-fremstillingsproces. Chipsene skabes ved at dyrke halvlederfilmen over toppen af ​​en wafer på en måde, hvor filmens krystallinske struktur er på linje med substratwaferens. Dette gør det vanskeligt at overføre filmen til andre substratmaterialer, hvilket reducerer dens anvendelighed.

Derudover udføres den nuværende metode til at overføre og stable disse film gennem mekanisk eksfoliering, en proces, hvor et stykke tape trækker halvlederfilmen af ​​og derefter overfører den til et nyt substrat, lag for lag. Denne proces resulterer i flere uensartede lag stablet oven på hinanden med hvert lags ufuldkommenheder akkumuleret i det hele. Denne proces påvirker kvaliteten af ​​produktet samt begrænser reproducerbarheden og skalerbarheden af ​​disse chips.

Endelig fungerer visse materialer ikke godt som ekstremt tynde lag. Silicium forbliver allestedsnærværende som det foretrukne materiale til halvlederchips, men jo tyndere det bliver, jo dårligere præsterer det som en fotonisk struktur, hvilket gør det mindre end ideelt i fotodetektorer. Andre materialer, der yder bedre end silicium, da ekstremt tynde lag stadig kræver en vis tykkelse for at interagere med lys, hvilket udgør en udfordring med at identificere optimale fotoniske materialer og deres kritiske tykkelse for at fungere i fotodetektorhalvlederchips.

Fremstilling af ensartede, ekstremt tynde fotoniske halvlederfilm af høj kvalitet af andet materiale end silicium ville gøre halvlederchips mere effektive, anvendelige og skalerbare.

Penn Engineers Deep Jariwala, adjunkt i elektro- og systemteknik, og Pawan Kumar og Jason Lynch, en postdoc og en ph.d.-studerende i hans laboratorium, ledede en undersøgelse offentliggjort i Nature Nanotechnology der havde til formål at gøre netop det. Eric Stach, professor i Materials Science and Engineering, sammen med sin postdoc Surendra Anantharaman, ph.d.-studerende Huiqin Zhang og bachelorstuderende Francisco Barrera bidrog også til dette arbejde. Samarbejdsundersøgelsen omfattede også forskere ved Penn State, AIXTRON, UCLA, Air Force Research Lab og Brookhaven National Lab og blev primært finansieret af Army Research Lab. Deres papir beskriver en ny metode til fremstilling af atomisk tynde supergitter eller halvlederfilm, der er meget lysemitterende.

Et-atom-tykke materialer har generelt form af et gitter eller et lag af geometrisk justerede atomer, der danner et mønster, der er specifikt for hvert materiale. Et supergitter består af gitter af forskellige materialer stablet ovenpå hinanden. Supergitter har helt nye optiske, kemiske og fysiske egenskaber, der gør dem tilpasselige til specifikke applikationer såsom fotooptik og andre sensorer.

Holdet hos Penn Engineering lavede et supergitter, fem atomer tykt, af wolfram og svovl (WS2).

"Efter to års forskning ved hjælp af simuleringer, der informerede os om, hvordan supergitteret ville interagere med miljøet, var vi klar til eksperimentelt at bygge supergitteret," siger Kumar. "Because traditional superlattices are grown on a desired substrate directly, they tend to be millions of atoms thick, and difficult to transfer to other material substrates. We collaborated with industry partners to ensure that our atomically thin superlattices were grown to be scalable and applicable to many different materials."

They grew monolayers of atoms, or lattices, on a two-inch wafer and then dissolved the substrate, which allows the lattice to be transferred to any desired material, in their case, sapphire. Additionally, their lattice was created with repeating units of atoms aligned in one direction to make the superlattice two-dimensional, compact and efficient.

"Our design is scalable as well," says Lynch. "We were able to create a superlattice with a surface area measured in centimeters with our method, which is a major improvement compared to the micron scale of silicon superlattices currently being produced. This scalability is possible due to uniform thickness in our superlattices, which makes the manufacturing process simple and repeatable. Scalability is important to be able to place our superlattices on the industry-standard, four-inch chips."

Their superlattice design is not only extremely thin, making it lightweight and cost effective, it can also emit light, not just detect it.

"We are using a new type of structure in our superlattices that involves exciton-polaritons, which are quasi-state particles made of half matter and half light," says Lynch. "Light is very hard to control, but we can control matter, and we found that by manipulating the shape of the superlattice, we could indirectly control light emitted from it. This means our superlattice can be a light source. This technology has the potential to significantly improve lidar systems in self-driving cars, facial recognition and computer vision."

Being able to both emit and detect light with the same material opens the door for more complicated applications.

"One current technology that I can see our superlattice being used for is in integrated photonic computer chips which are powered by light," says Lynch. "Light moves faster than electrons, so a chip powered by light will increase computing speed, making the process more efficient, but the challenge has been finding a light source that can power the chip. Our superlattice may be a solution there."

Applications for this new technology are diverse and will likely include high-tech robotics, rockets and lasers. Because of the wide range of applications for these superlattices, the scalability is very important.

"Our superlattices are made with a general, non-sophisticated process that does not require multiple steps in a clean room, allowing the process to be repeated easily," says Kumar. "Additionally, the design is applicable to many different types of materials, allowing for adaptability."

"In the tech world, there is a constant evolution of things moving toward the nanoscale," he says. "We will definitely be seeing a thinning down of microchips and the structures that make them, and our work in the two-dimensional material is part of this evolution."

"Of course, as we thin things down and make technology smaller and smaller, we start to interact with quantum mechanics and that's when we see interesting and unexpected phenomena occur," says Lynch. "I am very excited to be a part of a team bringing quantum mechanics into high-impact technology." + Udforsk yderligere

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