Micro Area Photocurrent Measurement System

With the development of micro nano photonics,it is necessary to characterize the micro optoelectronic performance of optoelectronic devices to improve the performance of existing optoelectronic devices and develop the next generation of optoelectronic devices.Photocurrent scanning microscopy(OCSM)is an effective method to characterize photovoltaic devices and photodetectors.It has been used to study the micro mechanism and improve the performance of various devices.However,it is difficult to distinguish the contributions of structural optics and electricity.In order to distinguish and quantitatively study the influence of structure optics and electricity,a micro area photocurrent measurement system is proposed in this paper.Taking Ga As solar cell as an example,the influence of micro nano structure on optics and electricity of photoelectric devices is measured by in-situ extraction of single wavelength micro area reflection image and single wavelength micro area photocurrent image,and by means of image feature extraction.The system is conducive to further reveal the interaction between light and matter at micro and nano scale,and provides a quantitative characterization method for the development of more efficient light trapping structures and photovoltaic devices,The specific work includes the following three aspects:1.Based on the characterization requirements of optoelectronic devices,the scheme design of micro area photocurrent measurement system is proposed,including the system hardware composition and software design.The design of the system is mainly divided into three parts:(1)the hardware of the system realizes the wavelength scanning and spatial scanning of nanometer laser,and integrates the common measurement of optogalvanic diagram and reflection map for the first time;(2)the system software design mainly includes:system software interface design,control system instrument program design,system software operation design;(3)based on the system hardware composition The data acquisition theory of micro area photocurrent measurement system is proposed,and the time resolution of micro area photocurrent measurement system is explained,and the mathematical formula that the system scanning time interval should be greater than the system time resolution is derived.2.According to the scheme design of micro area photocurrent measurement system,the software implementation of extracting micro area optogalvanic diagram module and extracting micro area reflection diagram module are completed respectively.When programming the two modules,the precise control of multiple instruments and the integration of multiple program modules are realized.It includes: laser,acousto-optic tunable filter system,electric displacement table,high-precision source table,spectrometer,optical imaging CCD instrument precise control,as well as the preparation of export data program,control lightfield software program,the preparation of corresponding wavelength reflection map data program.The system can realize the measurement of micro area optogalvanic diagram and micro area reflection map,and the spatial scanning accuracy is 500 nm,the optical scanning accuracy can reach 100 nm,and the wavelength extraction accuracy of single wavelength micro area reflection map can reach 100 nm.3.The data image processing algorithm in micro area photocurrent measurement system is studied.In order to extract single wavelength reflection image from full spectrum image,a wide spectrum image extraction algorithm is studied,and the function of extracting single wavelength image data from full spectrum image data is realized.At the same time,the optimal threshold range of the image optical density is calculated and analyzed based on the image processing algorithm of micro photocurrent and reflection image.4.The micro area photocurrent measurement system designed and built in this paper is tested.The feasibility of the system is verified by measuring and analyzing the single wavelength micro area photo current diagram and single wavelength micro area reflection diagram of single junction gallium arsenide battery.By comparing the two kinds of images with the scanning electron microscope(SEM)and the full spectrum reflectance of the sample cell,the single wavelength micro area photocurrent diagram and the single wavelength micro area reflection map reflect the dispersion and roughness of the two-dimensional distribution of the photoelectric conversion performance of the device surface,respectively.