LEDs that emit light with high brightness, long life, and low power consumption are widely used as light sources indispensable for daily life such as traffic lights, flat panel displays, and lighting.
Currently, nitride semiconductors and phosphide semiconductors are used for blue and red LEDs.However, these have the so-called "green gap problem" in which the light conversion efficiency is greatly reduced in the green region where the human visual sensitivity is the highest, and small size, high efficiency, high brightness, and high definition are required. In order to realize generation televisions and projectors, a completely new semiconductor material that emits green light with high efficiency is required.
This time, the research group of Tokyo Institute of Technology has succeeded in developing a new semiconductor "SrHfS3" that can control the electrical characteristics and emits green light at room temperature. An LED has a structure in which a p-type semiconductor in which an electron hole (hole) moves and an n-type semiconductor in which electrons move are joined, and a voltage is applied to this to recouple the holes and electrons to emit light. As we have obtained, SrHfS3 is said to have both p-type and n-type electrical conductivity.
In order to achieve both the two functions of p-type / n-type electrical conductivity and highly efficient green emission with a new material, this research group has (2) the use of nonbonding orbitals in highly symmetric crystals. (1) We proposed two chemical design guidelines: selection of a crystal structure with a direct transition type bandgap using band folding.As a result of screening candidate materials based on this, we arrived at SrHfS2, which is a perovskite-type sulfide.
The new semiconductor SrHfS3 can control p-type and n-type electrical conductivity by appropriate element substitution, and can emit green light that is visually bright even at room temperature.It is highly expected to be applied in the future as a next-generation green LED that solves the green gap problem.