Photodetectors are sensors that convert light into electricity. These technologies include cameras, solar panels and fiber optics. Photodetectors are becoming smaller and more affordable due to the shrinking of their semiconductor chips. However, current manufacturing techniques and materials are limiting miniaturization and forcing compromises between performance and size.
The traditional manufacturing of semiconductor chips has many drawbacks and limitations. The semiconductor film is applied to a wafer and then grown over it in such a manner that its crystalline structure aligns with the substrate wafer. This makes it more difficult to transfer the film onto other substrate materials, which reduces its usefulness.
The current method for stacking and transferring these films is mechanical exfoliation. This involves a piece or tape pulling off the semiconductor film, and then transferring it to a new substrate layer by layer. The result is multiple layers that are not uniformly stacked on top one another. This causes imperfections to accumulate in the final product. This can have an adverse effect on the product’s quality as well as limiting the chips’ reproducibility or scalability.
Some materials are not able to function well in very thin layers. While silicon remains the most popular material for semiconductor chips, it is less effective as a photonic structure. This makes it less suitable for photodetectors. There are other materials that perform better than Silicon, but they still need to have a certain thickness in order to interact with light. This poses the challenge of finding optimal photonic materials.
The production of uniform, thin, high-quality photonic semiconductor films from material other than silicon would increase the efficiency, application, and scalability of semiconductor chips.
Deep Jariwala (Penn Engineers) and Pawan Kumar (Postdoctoral Fellow and doctoral student in their lab, led a study that was published in Nature Nanotechnology. Eric Stach, Professor of Materials Science and Engineering, Surendra Anantharaman, Huiqin Zhang, and Francisco Barrera, a doctoral student, also contributed to this research. This collaborative study was funded primarily by the Army Research Lab. It also involved researchers from Penn State, AIXTRON and UCLA. The paper describes a novel method for producing atomically thin superlattices or semiconductor films that are extremely light emissive.
Materials with one atom thickness generally have the shape of a lattice. This is a layer of atoms that are aligned in a specific way and form a pattern. A superlattice is a combination of layers of different materials that are stacked on top of each other. Superlattices are unique in their optical, chemical, and physical properties. They can be used for specific applications like photo optics or other sensors.
Kumar says that after two years of research and simulations that showed how the superlattice would interact in the environment, it was time to experiment with building the superlattice. Traditional superlattices are created on the desired substrate and can be difficult to transfer to other substrates. Our superlattices, which are atomically thin, were developed in collaboration with industry partners. They can be scaled and applied to many materials.
On a two-inch wafer, they created monolayers of atoms or lattices. The substrate was then disintegrated, which allows the lattice transfer to any material desired, in this case sapphire. Their lattice also contained repeating units of atoms that were aligned in one direction. This made the superlattice compact, two-dimensional and efficient.
Lynch says that Lynch’s design can be scaled. Lynch says that the method he used was able to create superlattices with a surface area of only centimeters. This is an improvement over current silicon superlattices made at a micron scale. Because our superlattices are uniformly thick, this allows for easy and repeatable manufacturing. It is crucial to scale our superlattices to fit on industry-standard four-inch chips.
The superlattice design of their superlattice is extremely thin and light weight, so it can emit light instead of just being detected.
Lynch says that Lynch is using a new structure in superlattices. It involves exciton polaritons. These quasi-state particles are made up of half matter and half sunlight. Although light is difficult to control, we can control matter and found that we could manipulate the shape of the superlattice to indirectly control the light it emits. Our superlattice can also be a light source. This technology could significantly improve the lidar systems of self-driving cars, facial identification, and computer vision.
The ability to emit and detect light from the same material opens up new possibilities for complex applications.
Lynch says that integrated photonic chip powered by light is one current technology where Lynch can see our superlattice used. The speed of light is faster than electrons so a chip powered with light will improve computing speed and make the process more efficient. However, the challenge was finding a light source to power the chip. The superlattice could be the solution.
This technology has many applications. It will most likely be used in high-tech rockets, robotics, and lasers. The scalability of these superlattices is important due to the many applications they can be used for.