Research On Deep-Subwavelength GaAs Nanowire Photodetectors Based On Dipole Antennas

Semiconductor nanowires have important application potential in ultra-small photodetectors.However,limited by the optical diffraction limit,further reduction of the size of the nanowire photodetector to increase its integration has encountered bottlenecks.Localized surface plasmons can limit the optical field to sub-wavelength range,which is an effective way to break the optical diffraction limit.In this paper,a deep sub-wavelength nanowire photodetector is designed by combining metal nano-antenna with GaAs nanowire.The main research results are as follows:(1)The light absorption characteristics of GaAs nanowire photodetectors are theoretically studied by finite time domain difference method.The results show that the light absorption of the nanowire photodetector is based on the leakage mode resonance effect.As the diameter of the nanowire decreases,the light field limitation becomes weaker,and the light absorption efficiency and responsivity of the detector are reduced rapidly.At a diameter of 20,40,and 60 nm,the responsivity of the device is 0.006,0.024,and 0.034 A/W,which is only 4.5%,18.2%,and 22%of 90 nm(0.132 A/W).(2)In order to improve the performance of small-diameter nano wire photodetectors,a GaAs nanowire light detecting cone based on metal dipole antenna is designed.By the mutual coupling of plasmon excitations in the metal dipole antenna with the absorption resonances of the nanowire,a hybrid system formed by the semiconductor nanowire and the dipole antenna increase its absorption ability of light.The results show that the dipole antenna has a significant effect on the absorption of nanowires with its diameter is in the range of 20～90 nm.The responsivity of the device is increased to 1.74-4.14A/W,which is 13～576 times higher than that the structure without antenna.(3)Exploring the parameter of angle and size of the dipole antenna to further optimize the performance of device.The results show that when the cone angle of the antenna is 0°,the detector has the highest detection responsivity,that is,the rectangle is the optimal antenna shape of the nanowire detector.For nanowire with a diameter of 20 and 60 nm,the corresponding optimal width of the antenna are 30,50 nm respectively.Accordingly,the optimal responsivity is 6.74,7.64 A/W respectively.Compared with no antenna,it is enhanced by 1123.3,224.7 times respectively.