Silicon Nitride Based Nanobeam Cavity And Its Applications

One dimensional photonic crystal(PhC)namobeam cavity with the photonic band gap along the direction of light propagation has the advantages of high quality factor,small mode volume and strong light matter interaction.These advantages make the namobeam cavity structure suitable for the basic unit of sensor and light source.The development of sensors and light emitters are mainly in the infraredrange and the devices working at visible light band are attractive in recent years.Wide-bandgap Silicon nitride material which is regarded as the alternative material for silicon has the advantages of wide transparent spectrum bands from visible to mid-infrared,complementary metal oxide semiconductor(CMOS)compatible and lower propagation loss than silicon.It is considered to be the primary platform for the visible photonic devices.In this paper,devices based on nanobeam cavities were fabricated on a silicon nitride platform for realizing visible-light high-performance photonic devices,such as a refractive index sensor and a light emitter.Firstly,we design and fabricate suspended silicon nitride nanobeam cavity based visible light emitters with colloidal quantum dots.Energy band theory and the finite time domain difference method(FDTD)method are used to design the nanobeam structure.The suspended silicon nitride nanobeam cavity array working at the wavelength of 630nm is fabricated using the electron beam lithorgraphy followed by dry etching and wet etching.The colloidal quantum dots CDSe/ZnsS are successfully transferred to the surface of the nanobeam cavity and the simulated spontaneous emission enhancement factor of quantum dots is estimated to be 5.26.The spontaneous emission fluorescence is measured by applying modulated continuous blue pumping laser and the fluorescence collection and micro imaging are characterized.We also design and demonstrate the visible light refractive index sensor based on suspended silicon nitride nanobeam cavity.The finite element method and FDTD method are used to design the high-order silicon nitride based nanobeam cavities working at 710nm.The calculated Q factor maintains to be larger than 1100 over a large range of refractive index of NaCl solutions and the sensitivity is calculated to be 314nm/refractive index unit(RIU).The suspended nanobeam cavity structure is fabricated by electron beam lithography(EBL)followed by inductively coupled reactive ion etching and wet etching.Negative photoresist maN-2403 is used as the etching mask to ensure high resolution nanobeam cavity structure and also effectively solve the problems poor resistance to etching.The fabricated device is then emerged into the NaCl solitons with different concentrations to obtain the measured Q factor and sensitivity with the variety of cladding refractive index and the fitting line shows the sensitivity is 321 nm/RIU,which is the largest value among the resonators based visible light refractive index sensors.