The Simulation Of ZnO-based MSM Schottky Type Ultraviolet Photodetector

Owing to great advantages of low dark current,fast response speed and easy to integrate,ZnO based metal-semiconductor-metal(MSM)Schottky type ultraviolet photodetector(UV PD)has broad application prospect on the aspects of the missile tracking,UV communication,fire detection and alarm and become one of the hot topics in the study of ZnO ultraviolet detector.The MSM structure has a negative effect on the photoelectric performance of the device due to the shading effect of the incident light.The photoelectric performance of the detector can be improved effectively by selecting reasonably structure parameters of the device,using the asymmetric structure and the new electrode structure.In view of the current research situation of ultraviolet detector at home and abroad,the paper launches a system research from the physical modeling,simulation analysis and structure optimization using Atlas module of the simulation software Sivaco,and has obtained the following research results:Firstly,based on the theory of thermal electron emission,the physical model of MSM ZnO Schottky type ultraviolet detector is established.A device with 13?m electrode width and 8?m electrode spacing is simulated.The results show that dark current is 8.59×10-10 A at 1V bias and photocurrent is three orders of magnitude higher than dark current;Peak value of spectral response is 0.066A/W and corresponding cutoff wavelength is 370 nm and response drops sharply in the range of 370nm~600nm.The effects of the structure parameters such as the thickness of the epitaxial layer,the carrier concentration and the size of the electrode on the I-V characteristics of the detector are studied.Simulation results show that the I-V characteristic is greatly influenced by the structural parameters.detector is with maximum quantum efficiency of 47.4%,the highest response 0.141A/W and higher light dark current ratio 61174 under 10 V bias,when epitaxial layer thickness is 0.5?m,carrier concentration is 1×1015cm-3,electrode width is 1.5?m and electrode spacing is 2.5?m.Secondly,the simulation results show that dark current of the ZnO based MSM-PD can be reduced by the asymmetrical work function.By studying the normalization photo to dark currentratio(NPDR)of detector at 10 V bias voltage,asymmetric structure Ag/ZnO/Pd MSM-PD obtains highest NPDR,and higher approximately an order of magnitude compared to symmetric structure Ag/ZnO/Ag;Similarly,dark current characteristics of asymmetric area contact electrode of ZnO based MSM-PD also have inhibitory effect.Under 10 V bias,for detector with the same total electrode contact length and electrode spacing,with asymmetric contact area(as well as asymmetric contact length)the ratio increasing to 1:7,dark current decreases about 2times.As the electrode spacing is kept constant,the photocurrent are not affected;and with the increase of the degree of asymmetry of the electrode,PDR increases.Finally,the simulation model of triangular electrode MSM-PD is established,and its I-V characteristics are simulated.The results show that photocurrent of triangular electrode is increased by 58.3% compared to the traditional MSM-PD,while dark current is not significantly increased.The effect of triangle electrode angle,electrode spacing and electrode width on incident light plays an important role.Optimization results show that under 15 V bias and 370 nm illumination,60 o electrode bottom angle,2?m electrode width and 2.5?m spacing of the detector achieves optimization and has larger optical dark current ratio,high quantum efficiency and responsiveness,which is 53500,79.3%,0.238A/W.In the same,the simulation model of the semi-circle electrode MSM-PD is established,and the influence of the detector electrode size on the spectral response is studied.In order to achieve the best photoelectric detection performance,the structure of the semi-circular electrode is optimized.The optimization results show that the detector has the largest response degree 0.170A/W near the 370 nm,and the corresponding external quantum efficiency is 55.5%,when the electrode radius is 0.5?m and the electrode spacing is 2?m.