Research Of The Sensitivity Of GaAs-Based Photoconductive Semiconductor Switches

Photoconductive Semiconductor Switches(PCSS's)own a comprehensive application in the fields of high power ultra-wideband pulses and ultra-fast electronics owing to their superb optical and electrical characteristics.GaAs-based PCSS's have the higher voltage-resistant and more fast response speed which let them be the dominant PCSS's.As switch devices,the measuring standards of PCSS's should conclude response speed,voltage-resistant and sensitivity.Among them,the most important one is about sensitivity which contributes to the capacity of conduction.This article focus on how to improve the sensitivity of switches including the enhancement of the ability of light absorption and current transmission.The main contents of this research program as follow:In order to increase the percentage of light entering the devices,we design the anti-reflection coating containing single layer and bilayer on the top of devices.As to the laser of which the wavelength is 905 nm and the GaAs wafer possessing the refractive index of 3.46,the optimal thickness value of SiNx single layer antireflection coating is 110 nm which refractive index is 1.86.Moreover,bilayer antireflection coating conduct a better result that single layer.All those kind of antireflection coatings can improve the sensitivity of PCSS's.And we can increase the thickness of SiNx which are odd times of basic thickness to ensure the high voltageresistant.We design the back-reflector to let the transmission light reflect back to devices.In this article,we choose the Ag film as the single back-reflector which boosts the capacity of light absorption and the amount of sensitivity increase is about 0-100%.Furthermore,inserting a Nano-dot layer between the wafer and Ag film can enhance the adhesive force between them and prevent agglomeration of Ag film which can improve the sensitivity of PCSS's further.With the purpose of measuring the relationship between structure of electrodes and sensitivity,we analyze the sensitivity of different electrodes gaps and electrodes shapes to make characterization.The result shows that when the gaps decrease from 8mm to 2mm,the conducted current will be higher which indicates the smaller are the gaps,the better sensitivity they are.However,with the limitation of laser,the gap of 2mm has a lower utilization ratio of light energy.So the gap optimal value is between 2mm and 4mm.In the meanwhile,the shapes of electrodes can influence the electric field distribution between electrodes.And in this article,the most concentrated one is circle which has the lower energy loss and better sensitivity.All in all,designing anti-reflection coating and back-reflector structure and adjusting the gaps and shapes of electrodes can improve the sensitivity of PCSS's.Then we can take other parameters such as the capacity of voltage-resistant into account to optimize better structures of devices.