Study On The Fabrication And Optical Properties Of GaN-based Microrods

?-Nitrides are widely used in the field of light-emitting devices because ?Nitrides are typical direct band gap semiconductor materials,which have continuously adjustable band gap.However,the quantum confined Stark effect brought by polarization and the high refractive index of the material itself result in the low luminous efficiency of the planar structure.The cylindrical structure can change the light exit angle and relieve the polarization effect caused by stress.In order to improve the internal and external quantum efficiency,the cylindrical surface structure has attracted wide attention in improving the luminous efficiency of LEDs.GaN microcavity lasers have broad application prospects in the fields of optoelectronic integration and biosensing due to the advantages of small size,high quality factor,narrow line width,and low loss.Because of its good confinement ability on photons,the photon density in the microcavity is very high and the possibility of interaction between photons and matter is improved.Therefore,it plays an important role in the frontier theoretical research of advanced optoelectronics.When the photon is confined in the microcavity,the photon will propagate along the sidewall and be totally reflected,forming a whispering gallery mode and causing photon oscillation.At present,the microcavity lasers that have been successfully implemented include microrings,microdisks,etc.The preparation process of these microcavity structures is often relatively complicated.But the micro-pillar preparation process is simple,not only is it possible to form photon oscillations,but the cylindrical structure itself has the effect of improving the internal and external quantum efficiency of the LED.In this paper,around the optical mode of GaN micropillars,the optical properties of Ga N micropillars are studied through theoretical calculations and experimental tests.The main contents and results of the research are as follows:(1)Based on the sapphire-based GaN-LED,micro-pillars of different diameters were successfully fabricated and related process parameters were optimized.After replacing the etching gas Cl2 with Ar and reasonably adjusting the etching gas flow ratio,a micro-pillar perpendicular to the substrate was successfully fabricated.And based on the difference in the corrosion rate of the different crystal planes of Ga N by the alkaline solution,the etched sidewalls were modified by the KOH solution to smooth the rough sidewalls.GaN-LED micropillars with regular shapes and smooth sidewalls were fabricated finally.(2)The optical properties of the prepared micro-columns were measured,and the optical properties of the same micro-columns under the excitation of variable power light sources were obtained.The non-linear relationship between excitation intensity and optical power density indicates that the photon produces resonant lasing in the micron column.When the optical power density exceeds the threshold,three obvious lasing peaks appear on the PL spectrum and the lasing peak positions are 420.6 nm,426.8 nm,and 433.2 nm.The excitation intensity increases successively,and the respective power density thresholds are4.023 k W/cm2,3.816 k W/cm2,3.429 k W/cm2,respectively.The resonance mode of the micrometer column was analyzed by the finite difference time domain method,and the resonance mode in the micrometer column was determined to be the transverse whispering gallery resonance mode.(3)In addition,the optical properties of the micro-columns before and after the KOH solution modification were compared.The results show that the spectral intensity of the micro-column modified by the KOH solution is greatly improved,and optical resonance occurs in the cylindrical microcavity.Finally,the optical properties of the micron columns with different diameters were compared.Within a certain range,when the diameter of the micron columns is smaller,the wavelength of the strongest resonance peak is larger and the threshold is lower.