The Design Of Minority Carrier Lifetime Measurement System Based On Cylindrical Resonator Disturbance Method

The minority carrier lifetime of semiconductor materials is an important index to evaluate the performance of semiconductor devices.Among many minority carrier lifetime measurement techniques,microwave photoconductivity testing is widely used because of its high accuracy,no contact and instant measurement.Microwave resonator is a special sensor with the advantages of high precision,strong anti-interference ability and high sensitivity.The microwave resonator can detect the material permittivity,permeability and related physical processes by using the perturbation detection theory and the output power variation of the resonator sensor.Based on the microwave resonator perturbation theory,the objective of this study is to realize the measurement of the non-equilibrium carrier transient dynamics of semiconductor after photo-excited by cylindrical resonator.The microwave perturbation method is described in detail in theory.Combined with the energy level structure theory of semiconductor,the photo-generated carriers are divided into free carriers and trapped carriers.This work focuses on resonator design,coupling,and impedance matching regulation without specifically distinguishing between photoconductivity and photo-dielectric.In the design of resonator sensor,the electromagnetic field morphology and distribution mode in the cylindrical cavity are analyzed by electromagnetic field theory.Two brass cylindrical resonator with surface gold plating with different quality factors are designed,respectively,resonant TE₀₁₁ and TM₀₁₂12 mode.The coupling mode design of resonator is carried out by using the HFSS software recognized by the industry as the electromagnetic simulation platform.The discussion and simulation of rectangular hole,circular hole and antenna coupling are carried out.The coupling hole parameters affecting the coupling effect and the waveguide length of the transmission microwave are analyzed and optimized.The reflection coefficient of the resonant system using rectangular coupling hole is attenuated at about-30dB,which has good resonance effect.The no-load quality factor of the resonator can reach about 16000 and has high sensitivity.A single-branch equalizer is used to adjust the coupling of the resonator and the time resolution of the whole system,and the effect is simulated.Finally,a system is built for measuring photo-generated carrier dynamics of semiconductor materials.According to circuit theory,the test limit of the system is related to the quality factor and resonant frequency of the load cavity.The measurement of photo-generated carrier dynamics of several commonly used optoelectronic materials:silver iodide,anatase titanium dioxide,perovskite,and cadmium sulfide verified the system performance and obtained theoretically expected results,indicating that the system can effectively collect the photo-generated carrier dynamics process of the samples.The exponential decay or Gaussian morphology of the signal curve is related to the resolution of the instrument and the sensitivity of the system.The ideal photoconductive signal should take the form of exponential attenuation.The resonator with high quality factor increases the sensitivity of the system but also reduces the time resolution of the system,resulting in the Gaussian curve morphology of the photoconductive signal.The time resolution of the system is in the order of nanoseconds and can be adjusted appropriately for the measurement of the transient dynamics of photo-generated carriers in semiconductor materials with different kinetic attenuation constants.