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New Insights into Amplified Spontaneous Emission in 2D Semiconductors
Amplified spontaneous emission (ASE) is a phenomenon where light emitted by excited particles undergoes amplification, driven by photons of the same frequency inducing further emissions. This critical process underlies a variety of optoelectronic applications such as lasers and optical amplifiers, which enhance light intensity.
The interaction of high-energy photons with a material can lead to the formation of an electron-hole plasma, a condition marked by a dense mixture of electrons (negatively charged particles) and holes (the absence of electrons, treated as positively charged). Recent research from Wuhan University has documented the occurrence of ASE from degenerate electron-hole plasma in a two-dimensional semiconductor known as suspended bilayer tungsten disulfide (WS2). Their findings, detailed in a paper published in Physical Review Letters, herald potential advancements in the development of innovative optoelectronic technologies harnessing 2D semiconductors.
“This study builds on prior investigations into highly excited states in transition metal dichalcogenides, where we noticed an unusual surge in photoluminescence (PL) intensity upon reaching a certain threshold of excitation power,” explained Yiling Yu, the paper’s senior author. “This suggested a notable phase change in the excited electron-hole system, which we believed could drastically alter the optical dielectric function.”
The primary aim of Yu and her team was to dissect the changes in the dielectric function correlated with the PL intensity spike identified in earlier studies. Additionally, they sought to elucidate the physical mechanisms fueling this phase transition related to enhanced PL.
“To achieve our goals, we employed two significant experimental approaches,” Yu clarified. “Initially, we conducted transient differential transmission spectroscopy on bilayer WS2 subjected to continuous-wave laser excitation, enabling us to observe optical gain coinciding with a pronounced rise in PL intensity.”
Following their initial findings, the researchers aimed to identify the source of the ASE observed in WS2. They measured the photoluminescence spectrum of a sample integrated with a Fabry-Pérot cavity, revealing characteristics consistent with an electron-hole plasma phase.
“These experiments confirmed that both the optical gain and the ASE stem from the electron-hole plasma state within the highly excited WS2 configuration,” Yu noted.
The pivotal outcome of this research is the verification of ASE originating from degenerate electron-hole plasma in 2D semiconductors, an observation made for the first time. Moreover, the researchers gained valuable insights into how the optical dielectric response evolves during the phase transition of the excited electron-hole system.
“The ability of strong many-body interactions to sustain the degenerate electron-hole plasma and produce optical gain highlights the prospect of this excited electron-hole phase achieving new macroscopic quantum states,” Yu suggested. “This has the potential to enhance both fundamental knowledge and the practical applications in optoelectronics.”
The insights from Yu and her colleagues may catalyze further investigations into ASE within 2D semiconductors, potentially leading to groundbreaking discoveries. The research could also influence the future design and development of advanced optoelectronics built on 2D materials.
“We intend to utilize this excited electron-hole phase as a foundation to pursue avenues toward superfluorescence and macroscopic quantum phenomena akin to Bardeen-Cooper-Schrieffer theory, as well as achieve efficient lasing by merging these plasma states with customized photonic structures,” Yu concluded.
More information: Yan Xu et al, Room-Temperature Amplified Spontaneous Emission in Two-Dimensional WS2 beyond Exciton Mott Transition, Physical Review Letters (2025). DOI: 10.1103/PhysRevLett.134.066904.
Source
phys.org