When the 2-D material graphene was discovered in 2004, it opened up the promise of super-efficient, ultra-light next-generation solar cells and other electronics. Well, they’re still working on that, and meanwhile other contenders are crowding into the 2-D field. The latest development comes in the form of a new 2-D semiconductor junction that is being billed as the thinnest (and strongest) possible.
Thinnest possible heterojunction courtesy of University of Washington.
We Built This Thinnest Possible Semiconductor Junction!
Let’s get that group hug thing out of the way first. The new 2-D semiconductor junction was announced yesterday by the University of Washington (State, not DC), which partly funded the research with an extra assist from us taxpayers via the Department of Energy.
Go, team!
The research team included the University of Hong Kong and the University of Warwick, so also chipping in were the Research Grant Council of Hong Kong, the University Grants Committee of Hong Kong, the Science City Research Alliance (a partnership between Warwick and the University of Birmingham), the Higher Education Funding Council for England’s Strategic Development Fund, and the Hong Kong based Croucher Foundation.
(Not) Movin’ Kind Of Slow At The Junction
Hey, remember that old TV show Petticoat Junction? Well, the new 2-D semiconductor junction is kind of the same thing only faster and without the petticoats. It’s a type of heterojunction, which refers to the interface between two different kinds of semiconductor materials.
If that sounds a bit more complicated than it needs to be, it is. Heterojunctions have attractive properties in terms of efficiency, but they add complexity and expense to electronic devices, so until now they mostly pop up in specialty uses such as lasers.
If you’re thinking heterojunctions are also playing a role in improved solar cell efficiency, you’re on the right track.
A Super Cheap Self-Assembling 2-D Semiconductor Junction
The Obama Administration has been going all out to bring the cost of solar power down, with initiatives that run the gamut from improving solar cell efficiency to cutting installation costs and promoting new financing and energy efficiency programs.
The new 2-D semiconductor junction research comes under foundational work contributing to that first category, and here’s senior author Ziaodong Xu of the University of Washington enthusing about the potentials:
Our experimental demonstration of such junctions between two-dimensional materials should enable new kinds of transistors, LEDs, nanolasers, and solar cells to be developed for highly integrated electronic and optical circuits within a single atomic plane.
The demonstration involves two single-layer compounds that share similar structures, molybdenum diselenide and tungsten diselenide.
When combined, the two materials bond into a single, distinctive honeycomb lattice structure, which according to the team consists of “the strongest possible link between two single-layer materials.”
As for how this combination is achieved, all you need is a small furnace that can heat to 900 degrees Celsius, some hydrogen gas (renewable hydrogen, we hope), and the aforementioned two materials in powder form.
You put mix the two powders together, throw them in the oven, shoot some hydrogen gas through them, and let the magic happen.
When the gas passes through the oven, it carries off evaporated atoms from one of the powders and plunks them down in a cooler region, where they reform as three-sided, atom-thin crystals.
Evaporated atoms from the other powder follow in short order and attach themselves to the edges of the crystal, and there’s your atomically seamless heterojunction, weighing in at just three atoms thick.
That’s triple the thickness of graphene for those of you keeping score at home, but the important thing is that the self-assembling aspect of the process lends itself to cost-cutting, and the team foresees the potential for scaling up.
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