Simulation And Experimental Study Of Diamond Photoconductive Devices

Because of its excellent physical and chemical properties,diamond has become a promising material that can cope with harsh conditions and stringent requirements.Ultra-wide bandgap and high carrier mobility are important conditions for its use as a substrate material for deep ultraviolet detectors and photoconductive switches.The progress of single crystal growth diamond technology reduces the cost of diamond and paves the way for its application as optoelectronic devices.At present,the research on those applications of diamond is still in the ascendant,but it is still deficient in analyzing the mechanism of these devices,and nowadays there are few studies on diamond photoconductive switches.To this end,a photoconductive device based on a CVD diamond substrate is prepared in this paper.The working mechanism and operating characteristics of the device as a deep ultraviolet detector and photoconductive switch are analyzed by experiments and simulation.The main work of this thesis is as follows.(1)This paper proposed a model for the simulation of diamond photoconductive devices in Silvaco.Because the simulation of these devices is rarely introduced home and abroad and there also are no models in these simulation tools,one of the significant tasks and innovations of this article is to establish a simulation model of diamond photoconductive devices.The model is based on simulation experience and experimentally measured parameters of other diamond devices.It specifically introduces some models:,which include temperature-dependent band gap model,impurity and trap model,mobility model related to temperature,doping and electric field strength,light absorption model,impact ionization model,and illumination model.(2)In this thesis,we fabricated a CVD diamond substrate-based photoconductive device,and finished dark and light response tests of the device.The light source includes visible light and ultraviolet light at 185 nm,254 nm,and 365 nm.Two kinds of electrode structures have been fabricated.Among them,the large coplanar electrode structure has better performance,its dark current is less than 1 pA,its light response at 185 nm reaches137 nA,and its suppression ratio of 185 nm against visible light is as high as 6×10~5,which indicates that the influence of the visible light on the device is very weak.Therefore the device can be used as a visible-blind deep ultraviolet detector.(3)This thesis used the established simulation model to complete the simulation fitting of foreign literature and this experiment.Firstly,the experimental results of the reported thin-film DUV detector are reproduced,and it is determined that the influence of space charge limiting current effect resulted in the power-law relationship of its dark I-V characteristics and the concentrated distribution of photocurrent in the space charge region.After that,the experimental results of this paper are fitted by simulation.The simulation results show that metal impurities causes an increase in the concentration of surface traps,which leads to a decrease in the light response of the device and deteriorates its performance.It is also obtained that the external quantum efficiency of the coplanar device varies in an inverted U shape with increasing wavelength,with a peak value of 210 nm.(4)This thesis has finished simulating and analyzing the working characteristics of diamond photoconductive switches with different structures.For coplanar electrode devices,the maximum bias voltage in the dark state is 41KV,and the electric field is concentrated on the inside of the anode,causing breakdown at the surface of the device.Moreover,its light response to 213 nm is better than that to 224 nm,and the peak photocurrent of the former is 6 times that of the latter.The simulation results show that the maximum bias voltage can be increased by up to 40%and the photocurrent can be increased by 10%with a heavily doped layer under the anode.For vertical electrode structure,the electric field is uniformly distributed in the longitudinal direction,and it leads to a higher blocking voltage than that of the coplanar electrode devices.The maximum bias voltage in the dark state is 96KV.And because of its electrode structure and uniform internal electric field distribution,its light response to 224nm is better than that to213nm,and the peak photocurrent of the former is two orders of magnitude higher than that of the latter.