Fabrication And Optical Properties Study Of Rolled-Up Tubular Whispering Gallery Mode Microcavities

The self-rolld-up microtube is a three-dimensional tubular functional structure fabricated by self-rolled-up micro-nano technology.The self-rolled-up microtube has exhibited promising prospects in optoelectronic integration,microfluidic control,liquid sensing,biomedicine,owing to its smooth wall cavity,hollow features,integrated controllability.According to different materials,microtubes can be divided into passive microtubes(e.g.Si/SiO2 or SiOx/SiNx microtubes)and active microtubes(e.g.InGaAs/GaAs microtubes).Active microtubes are usually rolled-up from III-V semiconductor materials which embedded the gain mediums such as quantum wells(QW),quantum dots(QDs)in the active microtubes can significantly enhance its luminescence characteristics,and then qualify them as active whispering gallery mode(WGM)optical microcavities.Currently,according to the research on liquid sensing using rolled-up tubular microcavities the sensitivity of passive microcavities is limited within only a few hundred,which fails to meet the requirements of practical application.Consequently,it is of great significance to fabricate rolled-up tubular microcavities with higher Quality factor and to significantly improve their liquid sensing properties(sensitivity and detection limit).In this thesis,a series of experiments were performed with the aim to fabricate high Q factor GaAs/InGaAs self-rolled-up tubular microcavities embedded with InAs quantum dots(QDs)and do the research on its optical properties and the liquid sensing based on InGaAs/GaAs active microcavities.Main experimental contents and results include the following:1.Bilateral self-rolled-up microtubes and U-shaped mesa self-rolled-up microtubes were fabricated by the epitaxial structure,which was fabricated by embedding single QDs,sandwiched by two Al0.25Ga0.75As barrier layers,in the InGaAs/GaAs strained-layers structure.Microtubes with fine structure and excellent rolling downside length laid a solid foundation for the research on its optical and liquid sensing properties.2.The bilateral self-rolled-up microtubes were transferred to the SiO,substrate and WGM was obtained by micro-photoluminescence(?-PL)test.The U-shaped mesa self-rolled-up microtubes were tested by ?-PL test and WGM was obtained.The Q of self-rolled-up microtubes was calculated and some reached 1000.Further experiments were conducted to improve the value of Q by raising the height of the tubular microcavities with Au pad which is deposited between the two side pieces of the U-shaped mesa.Finally,we have successfully fabricated an optically-pumped InGaAs/GaAs quantum dot microtube laser at room temperature.3.The self-rolled-up tubular microcavities,fabricated by U-shaped mesa,were placed in air(RI:1.00),deionized water(RI:1.33)and alcohol(RI:1.36)and were tested by ?-PL test.The peak positive of WGM optical microcavity had significant shift,showing good liquid sensing properties.4.Self-rolled-up tubular microcavities were immersed into NaCl solutions with different degrees,which had been labeled with corresponding refractive indexes by use of Abbe refractometer.The curve of sensing properties was obtained by performing the ?-PL tests on the microtubes in the NaCl solutions.The corresponding sensitivity and detection limits were calculated.The self-rolled-up tubular microcavities have the liquid sensitivity of 3 093 nm/RIU and detection limit of 1.0×10-5 RIU.It has been demonstrated that the concentration change as tiny as 0.03 M(mol/L)of low salinity NaCl solutions can be distinguished by self-rolled-up tubular microcavities,which basically meets the requirements of NaCl detection for food.