Photoelectric Devices Based On Nanowire Arrays

In recently years,semiconductor nanowires have attracted great attention in the field of photoelectric devices due to their unique one-dimensional structure as well as their excellent optical and electrical performance.Compared with traditional th in-film structures,semiconductor nanowire arrays show great potential in low cost and high performance photoelectric devices due to their better anti-reflection effect and lower filling ratio.In the present thesis,theoretical and experimental studys about photoelectric devices based on semiconductor nanowire arrays are carried out.The main works are summarized as follows:(1)An innovative solar cell based on inclined GaAs p-i-n nano wire array is designed and the absorption and photovoltaic performance are analyzed.The results show that,compared with vertical nanowire arrays,the inclined nano wire arrays show stronger optical resonances and more effective absorption,which can suppress the recombination loss in top p-regions and enhance the conversion efficiency.By optimizing the nanowire array structure,an efficiency of 16.4%can be obtained in inclined nanowire array solar cells,0.9%higher than that of their vertical conterpart.Similar results have been obtained in InP and Si nanowire solar cells,demonstrating the universality of the performance enhancement of inclined nanowire arrays.(2)Axial and radial GaAs/AlGaAs nanowire pin junction array solar cells are designed by using AlGaAs for the heavily doped p-regions instead of GaAs.The wide bandgap AlGaAs can reduce the recombination loss in heavily doped p-regions and the minority carrier recombination at the top contact,and enhance the optical generation in i-regions at the same time.The results show that,the efficiencies of the axial and radial devices are improved by 3.5%and 1.84%for unpassivated devices.While with proper passivation,the efficiency enhancements of axial and radial devices are 1.45%and 8.42%.(3)A GaAs/InAs nanowire/quantum dot hybrid nanostructure array solar cell is designed and analyzed through a coupled optoelectronic simulation.By growing multilayer InAs quantum dots on the sidewalls of GaAs nanowires,not only the absorption spectrum of GaAs nanowires is extended by quantum dots,but also the light absorption of quantum dots is dramatically enhanced due to the light trapping effect of the nanowire array.The calculation results show that,with the same material volume,the optical absorption of quantum dots in nanowire arrays is 4.6 times higher than that in thin film structures.By introducing quantum dots,the efficiency of a 500 nm GaAs nanowire array solar cell is increased from 10.07%to 10.74%.(4)A self-powered photodetector based on the graphene/GaAs nano wire Schottky junctions is fabricated by exploring the graphene transfer and contact process.At room temperature,the measured ideal factor and Schottky barrier height are 6.18 and 0.58 eV,respectively.And a short circuit current of 3.16 ?A and an open circuit voltage of 0.43 V are achieved under 532 nm illumination.The device exhibits a responsivity is 1.54mA/W at zero bias and a short response/recover time of 71/194 ?s at room temperature.