Electrons Race Down a Quantum Highway express
Imagine a superhighway where cars zoom along with barely a slowdown: that's what a layer of ultraclean semiconductor looks like, where electrons travel vast distances without a single collision. Scientists have built a transistor in which electrons run twice as fast as in any similar device before.
Usually, when you turn such a material into an electronic device, you inevitably scratch it, contaminate it, and heat it, and the road gets ruined. Here, they did things differently: all the steps for creating contacts and gates were done on a separate sapphire wafer, which was then flipped over and gently pressed onto the clean material. It's like building a bridge on the shore and then lowering it onto the road without touching the asphalt.
This trick preserved the perfect smoothness of the quantum layer. The electrons in it form a two-dimensional gas: they move only in a plane, like billiard balls on a perfectly flat table. Now that the road is unspoiled, physicists can run experiments they could only dream of before: for example, trapping electrons in clever quantum traps or creating devices sensitive to the slightest magnetic fields.
Original abstract
as written by the authors arXiv:2601.15418
We report the fabrication and operation of a source-drain-gate three-terminal field-effect electronic device with an electron mobility exceeding $$40\times 10^6$$ cm$$^2$$ / (Vs). Several devices were fabricated, with the highest achieved electron mobility obtained using a symmetrically-doped GaAs/AlGaAs quantum well forming a two-dimensional electron gas (2DEG) with a density of $$1.47(1) \times 10^{11}$$ cm$$^{-2}$$ and a pristine, pre-fabrication electron mobility of $$44(2) \times 10^6$$ cm$$^2$$/(\text{Vs}). To circumvent the well-known degradation of electron mobility during fabrication, devices were fabricated using a flip-chip technique where all lithographic processing steps were performed on a separate sapphire substrate. This method demonstrates the successful operation of various gate assembly designs on distinct 2DEGs without observable mobility degradation. This advance doubles the previous record for field-effect electronic device mobility and enables access to new regimes of quantum transport and applications that were previously unfathomable due to mobility limitations.
A mobility of 40 million cm²/(V·s) means an electron in such a material travels hundreds of micrometers without collisions, like an ant running several kilometers without ever tripping.