Biomimetic Radial Tandem Junction Photodetector With Natural Rgb Color Discrimination Capability

The three-dimensional(3D)structure of the retinal rod and cone cells,which play a crucial roles in detecting light signal and distinguish colors in human eye,is a masterpiece of Nature and the result of natural evolution over millions of years.This natural 3D retinal cell geometry can help us to achieve advanced biomimetic color sensing capability.It has been known that the cone cells in the retina can capture and absorb the incident lights thanks to its conical shape and a jungle-like array,which then distinguish the red(R),green(G),and blue(B)colors through three different opsins and their biochemical reactions.This thus provides an inspiration for us to construct a biomimetic multicolor sensor,based on hydrogenated amorphous silicon(a-Si:H)radial tandem p-i-n junctions(RTJ)fabricated on Si nanowires(SiNWs),mimicking the 3D radial rod or cone shapes of the retinal cells.This new type of RGB-color sensor is quite different from the color sensors used in conventional charge-coupled detection(CCD)in camera,which achieves color recognition by using an array of filters to distinguish different RGB colors.In this traditional design,three different CCD photodetector units are required to be integrated into single pixel unit to recognize RGB colors.Therefore,the integration density and the spatial resolution have reached in recent years a saturation.The use of a biomimetic radial junction photodetector array to achieve a RGB color sensing could represent a promising new direction,as the needs of color filters can be avoided,while the wavelength dependent absorption can be achieved via a resonant mode selection rules in the 3D antenna design.Specifically,the major research works and innovations in this thesis can be summarized as the three following points:1.Explored and optimized the process of vertical SiNW growth via a tin(Sn)catalyzed vapor-liquid-solid(VLS)growth in a plasma enhanced chemical vapor deposition(PECVD)system,and the fabrication of a-Si:H radial junction solar cell units.We systematically explored the influences of the key parameters of hydrogen treatment time/temperature,Sn film thickness,nanowire growth temperature/time,and doping characteristics on the growth morphology of nanowires.We further explored the effects of various parameters on solar cell preparation,including the thickness of the intrinsic absorbing layer,the p-type doping concentration,the n-type doping concentration,the density of the nanowire array and the annealing conditions.Finally,a high performance radial junction solar cell has been achieved,as a solid basis for manufacturing radial tandem junction photodetectors.2.Design and analyze the 3D RTJ structure and the spectral absorption modes by using finite element analysis suite of COMSOL RF module.The spectrum absorption range of the RTJ array spans from 300 nm to 700 nm,while the wavelength selective absorption within the radially stacked pin junctions can be tuned by the different layer thickness.The experimental results were analyzed and compared to the simulation models to develop an in-depth understanding and optimal structural design.3.Fabricated and demonstrated a new biomimetic radial tandem a-Si:H PIN junction(RTJ)photodetector structure constructed upon 3D SiNWs.A series of structural parametric investigations have been carried out to fine-tune the RTJ multilayer structure for achieving a balanced RGB color discrimination.Thanks to the unique wavelength-dependent light incoupling and absorption behavior in the cavity-like radial junction photodetectors,a full RGB color recognition has been accomplished in single RTJ cells.These results could indicate a new direction or strategy to implement a new generation of color-sensing photodetector applications.