题目：Bridging the terahertz gap with two-dimensional optoelectronics
时间：2018年11月28日 上午 9时
讲学内容：There is a strong demand for sources and detectors of electromagnetic radiation in the 0.1 - 10 THz range due to their diverse applications in wireless communication, medical diagnostics, radio-astronomy and other areas. The operation of semiconductor lasers in this frequency range is hindered by strong non-radiative recombination. On the other hand, the operation of wave generators using radio-engineering principles is hindered by growing resistive-capacitive delays.
In this talk, we will show that 2D electronic systems offer a unique opportunity to bridge the terahertz gap. From one hand, we shall show that in high-electron mobility systems (such as graphene and its bilayer) electrons can respond to terahertz waves as almost collisionless plasma demonstrating strong plasmonic resonances. This enables selective and voltage-tunable detection of THz waves using compact micron-sized graphene transistors. These transistors can also act as terahertz generators supporting plasmon instabilities and self-excitation under direct current. From the other hand, we shall show that several two-dimensional electron systems (graphene and mercury cadmium telluride quantum wells) host electrons that are weakly affected by non-radiative recombination due to peculiarities of their energy dispersion. Suppression of non-radiative processes in such materials is deeply linked to the impossibility of impact ionization in Dirac vacuum. This unique possibility has already enabled the demonstration of ultra-long wavelength (20 mkm) stimulated emission from 2D quantum wells, and promises true terahertz lasing in optimized structures.