LLNL deposits quantum dots on corrugated IR chips in a single step

Quantum dots hold significant promise for next-generation sensors and displays, but manufacturing hurdles often stand in the way of widespread use. Traditional methods struggle to evenly coat the complex, textured surfaces ideal for advanced devices, especially over large areas or in precise patterns. To tackle such hurdles, Lawrence Livermore National Laboratory researchers have conformally coated pyramid-textured infrared photodetector chips with dense, crack-free quantum-dot films in one pass. The method enhances photodetector performance by eliminating post-processing and delivering working devices, according to a study in Nanoscale.

Instead of spin-coating a slurry across a flat wafer, the LLNL team used electrophoretic deposition to steer charged lead-selenide quantum dots onto pyramid-textured silicon. The solvent carries short, conductive ligands, so the dots arrive already wired for charge transport, eliminating the crack-prone ligand-stripping step that normally follows. Because only biased regions pick up a coating, the electric field acts like a stencil that’s useful for building future multiband sensors. Prototype devices registered about 0.01 A/W responsivity at 1,200 nm and toggled in roughly 4.6 milliseconds.

The core advantage of this electrophoretic deposition technique, combined with in-solution ligand exchange, is the ability to create these high-quality, functional films in a single, efficient step. This not only simplifies the manufacturing process but also improves the electronic properties of the quantum dots by using shorter, more conductive ligands from the outset.

“By turning the electric field on or off, one can start or stop the deposition process,” said LLNL materials scientist Christine Orme in an announcement. This precise control means that because only the biased regions pick up a coating, the method doubles as a built-in patterning step, opening the door to stamping different-sized dots on the same chip for multiband infrared sensors down the road.
In the long run, the LLNL team plans to tap the selective-area coating capability of their method to deposit different sizes of quantum dots onto distinct regions of a chip. The hope is that the method could clear a path for highly integrated, compact imaging systems capable of detecting multiple wavelengths of light simultaneously. In turn, this could pave the way for further adoption of quantum dots in advanced biomedical sensing and security applications, where the technology already sees some use.