Lasing Behavior Of CdS Micro/Nanostructure And Multiwavelength Optical Waveguide Properties Of Array Structure

As a natural carrier of nanolaser,one dimensional semiconductor nanostructures have been widely studied because it can be act as the optical cavity and gain medium,simultaneously.At present,lasing behavior of one-dimensional nanostructures has been reported,such as ZnO,ZnS,GaN,CdS and CdSSe.Reducing the lasing threshold is an important research direction of nanowire laser device performance.In this paper,we found that the lasing threshold can be reduced in different gas environment.Different from some published paper,the lasing threshold is modulated by optimizing structural parameters or by means of the enhancement effect of the surface plasmon.The lasing experiment of CdS nanowires/nanobelts in the different gas environment illustrates that the lasing threshold shows a decreasing trend.It was reduced from 10.5 MW/cm² in air to 9.82 MW/cm²,8.25MW/cm² and 7.22 MW/cm² in Ar,N₂ and He environment,respectively.It is attributed to the transient polarization of molecular gas.In addition,the lasing behavior of different nanostructure reveals that the different cavity has an impact on the lasing behavior.For the CdS comb-like structure,duo to no fixed cavity,so only the amplified spontaneous emission was observed.However,there appear exciton-electron?ex-el?scattering and electron-hole plasma?EHP?lasing in the nanowires/nanobelts,respectively.The lasing behavior was observed by real-time ICCD images in comb-like structures and other low dimensional nanostructures.Meanwhile,using the ICCD images,the WGM and F-P lasing mode can be distinguished in nanowire/nanobelt structures.Besides,we also study the waveguide behavior of multi-branch CdS comb-like structure under the multi-wavelength injection.As an array structure of light emitting,it can be applied to high integrated photonic circuits.Based on the research of waveguide properties of CdS comb-like structure and combined with the corresponding STEM images,the growth mechanism of two comb-like structure shows obvious differences.For type I structures,branches are directly grown on the trunk.But for type II structures,branches are grafted on the trunk.By studying the waveguide behavior of multi-branch CdS comb-like structure under the multi-wavelength injection,we found that there are obvious differences between type I and type II comb-like structure.For type I comb-like structures,due to the larger absorption coefficient,the incident light which is close to band gap or larger than band gap can be absorbed and converted to photoluminescence and then it can be propagated in the waveguide.Compared to type I structures,the light guiding efficiency is lower in type II comb-like structures.The main reason can be attributed to the growth difference between the truck and branches.Furthermore,the multicolor tunable characteristic of the comb-like array structures was observed through increasing the pumping power.The emission color can be tuned from red to green.The carriers dynamic experiment demonstrates that the color tunable phenomenon is originate from the intensity change of the near band emission and the defects related emission.