Research On Read-out Efficiency Of Near Infrared Light Applied For QWIP-LED Devices

Quantum Well-Light Emitting Diodes(QWIP-LED)Infrared Up-conversion Devices converts mid-infrared light to near infrared signals,which can be read-out by large scale Si CCD directly.As its potential of being used as large scale,high quality as well as low power dissipation,QWIP-LED can be a new approach in infrared detection.Currently the study of QWIP-LED mainly focus on the improvement of QWIP efficiency.GaAs QWIP-LED efficiency is limited by the light extraction efficiency of LED,which is about 1% to 2% under room temperature.Therefore the enhancement of light extraction efficiency can improve imaging quality of QWIP-LED effectively.In this paper,by investigating on light extraction methods,the surface modification model and photon recycling model which can be applied to QWIP-LED are proposed,to research read-out efficiency of infrared light.Here are main contents:1.Research on microlenses array to enhance infrared light extraction efficiency.Using micro lenses array to change the surface topology structure,different diameter and fill ratio microlenses LEDs were fabricated by self-organized polystyrene spheres.The experimental result shows that,by reducing Fresnel loss through equivalent refractive index of micro lenses array and coupling between emitting light and microlenses array,structured LED has an enhancement up to 2.5 folds in read-out efficiency at a wavelength of 860 nm.2.Research on light read-out efficiency by particle coupling and particle scattering between Au particle array and infrared LED.When the size and period of nanoparticles are 200 nm and 880 nm,the read-out light intensity of structured LED has a peak intensity which is 1.37 to 3.3 folds than conventional LED under vertical detection and 3.97 to 6.97 folds under oblique detection.3.Research on the light read-out efficiency by one dimensional anti-reflection gratings.Using ITO as anti-reflection layer,the emitting light intensity enhances 33% under room temperature.Simulation results shows that the 1D antri-reflection layer gratings with 0.9?m period and 0.45 duty cycle enhances total transmission by 51%;Further,a simulation of double gratings in both dielectric and antireflection layer increased transmission up to 55% with 0.9?m period,600 nm width and 100 nm film thickness.4.Designed photon recycling model intergrated with surface plasmon resonance.By the near field enhancement of surface plasmon resonance,a structure which combines 1D Au gratings and dielectric gratings was proposed.By the enhancement in state density of photons in LED quantum well,this structure enhanced internal quantum efficiency and external quantum efficiency by 3.5 folds and 5 folds.As this structure changed the state density of photons,it can be applied to photon-recycling QWIP-LED devices to further increase detecting efficiency.