Research On The Manufacturing Process And Mechanism Of Silicon Nanowire Array Photodetectors

Due to the large specific surface area and unique forest structure,silicon nanowire arrays have excellent light absorption properties and function as core building structures of high performance photodetection.At present,the preparation technology of large-area silicon nanowire arrays is still immature,which limits the performance promotion of silicon nanowire array photodetectors.This paper focuses on the technical difficulties in the fabrication of large-area and uniformly distributed silicon nanowire arrays.The research on the preparation of silicon nanowires/arrays by metal-assisted chemical etching(MACE)was carried out,and the mechanism of the MACE reaction process was revealed.Silicon nanowire arrays with controlled diameter,length and density were fabricated.Research on reprocessing technology of vertical silicon nanowire has been carried out,achieving the controllable preparation of morphology-graded silicon nanowire arrays.Based on the above structures,high performance photodetectors have been designed and fabricated.The main research contents and results of this paper are as follows:1)A finite-difference time domain simulation model of the light absorption characteristics of silicon nanowires was constructed.The influence of nanowire structure parameters on reflection and absorption spectra was studied.It was found that the average light absorption rate of silicon nanowire arrays increased with array height;It was found that the diameter of silicon nanowire arrays had a correlation effect with array period.Period/diameter ratio 2:1 has a better light absorption performance;A morphology-graded silicon nanowire model was established.Through the optical field distribution,it was found that upper silicon nanowire can effectively capture photons,and under silicon nanowire can ensure a high material filling rate and effectively absorbs incident light.Under same height and period conditions,the light absorption rate of a morphology-graded silicon nanowire is 2.7% higher than that of ordinary silicon nanowire,achieving high light absorption rate 90.3% at a height of 2μm.2)The fabricating process and mechanism of MACE silicon nanowires were carried out.The effects of etching process parameters(oxidant,hydrofluoric acid concentration,etching time,temperature)on the morphology,surface quality and etching direction of silicon nanowires were studied;A method of controlling the morphology of silver catalyst by thermal annealing was proposed,realizing the preparation of different silicon nanostructures such as silicon nanowalls,silicon nanopores,and large-area,ordered silicon nanowires.Ordered silicon nanowires with diameters ranging from 30 to 100 nm and heights of 11.78μm were obtained.It was found that the silver nanodendritic structure plays key role in the preparation of ordered silicon nanowires.The loose structure ensures mass transfer of the solution and also restricts the lateral movement of silver nanoparticles under dendrites,so that they can be etched at same rate.3)Research on the preparation of highly ordered silicon nanowire arrays by nanosphere template method was carried out.Non-close-packed nanosphere templates with different spacing and diameters were prepared;The metal catalyst structure in MACE was optimized;Silicon nanowire arrays with controlled diameter,length and density were fabricated.The maximum aspect ratio of the silicon nanowire array is 52:1,whose diameter is 310 nm and array height is 16.12μm.The average light absorption rate of the silicon nanowire array is greater than 95%according to the tests.The relationship between the optical absorption characteristics of silicon nanowire arrays and their height、diameter was studied.It was found that the light absorption rate of the array increases with array height.However,arrays which have too high lenth can lead to nanowire clusters,resulting in the reduction of light absorption.It was found that,when the ratio of the period to the diameter of the array is 2:1,the average light absorption rate is the highest.4)A controllable preparation method of morphology-graded silicon nanowire arrays by adjusting silicon nanowire diameter with KOH solution was proposed.The effects of KOH solution concentration,reaction time,and array height on the diameter and morphology of the array were studied.Through MACE reprocessing of the adjusted array,morphology-graded silicon nanowire array with controllable upper and down segment diameters and lengths was realized.The average optical absorption rate of the morphology-graded silicon nanowire array is higher than 99.5%,reaching a high absorption rate 99.74% at a low height of 4μm.5)High performance silicon nanowire array photodetector was designed and fabricated.Through conventional semiconductor processes,metal-semiconductor-metal(MSM)type lateral surface photodetectors were fabricated.The influence of the height parameters of silicon nanowires on the performance of the detector was tested,and the performance differences of two different silicon nanowire detectors were compared.The better detection performance of the morphology-graded silicon nanowire array photodetector was verified.The light response time was less than 20 ms and the photoresponsivity reached 1.2A/W under 5 V bias,which is better than the peak responsivity of 0.55A/W of traditional bulk silicon detectors.