Study On The Equivalent Circuit Model Of Novel Photodetector

Recently,there is a strong interest toward the wide band gap semiconductor materials in the use of high speed optical electronic communications,because of these superior characteristics such as high electron velocity,high radiation hardness and excellent heat conductivity etc.MgZnO based Metal-Semiconductor-Metal(MSM)ultraviolet(UV)photodetector has been well developed in the fields of missile warning and pollution analysis etc.Compared with traditional photomultiplier and silicon based ultraviolet photodetector,MgZnO based MSM UV photodetector could select the wavelength automatically,thus it can work without the use of expensive filters.Although MgZnO based MSM photodetector has been well developed recently,it still has tons of problems about theoretical model need to be settled.As the key equipment in detecting UV,it has been extensively used in optical communications.However,the detector has shown a long fall time which may due to the crystal quality of the materials.As known,the long tail of the temporal response will lead to a degradation of the bandwidth,which may not be sufficient for the real applications of high speed optical communication.Besides of the fall time,the noise of the detector may also affect the performance.Meanwhile these noises cannot be eliminated completely.Thus,it is very important to build a novel and accurate equivalent circuit model to simulate and predict the noise characteristics of the device and furthermore lower the noise power of the UV photodetector.The main studies are as follows,1)The gain peaking technique and MgZnO based MSM device have been combined to build a novel equivalent circuit to improve the bandwidth property,include series gain peaking and enhanced gain peaking circuit model of MgZnO based MSM UV photodetector.The bandwidth property of MgZnO based MSM photodetector has been researched by considering both RC and transit limitation.The saturation velocity of the photodetector could affect the transit limitation of the device.To ensure the accuracy of parameters,the high-filed transportation characteristics of MgZnO are investigated by a three-valley ensemble Monte Carlo simulation combined with first principle calculations.Furthermore,the bandwidths of the photodetectors with various finger widths have also been discussed and researched in this paper.The results show that the gain peaking technique,especially the enhanced gain peaking can improve the bandwidth significantly.2)In order to predict the noise properties of the photodetector,a noise equivalent circuit model of MgZnO based MSM UV photodetector has been built.The noise sources of the photodetector are introduced by the intrinsic and parasitic resistances.Furthermore,the impact of series and enhanced gain peaking techniques on noise property of the photodetector are also been researched.In the end,the result shows that the thermal noise would determine the output current when the photodetector works in the high frequency region.And the noise power of the series and enhanced gain peaking circuits are also determined by the thermal noise,which are agreed with the original circuit.Moreover,it can also be found that series and enhanced gain peaking techniques would also make a difference to the thermal noise and shot noise properties,the techniques have a prominent impact on decreasing the noise power of the MgZnO based MSM UV photodetector besides of enhancing the bandwidth.This work is of good help for design MgZnO MSM UV photodetector with good properties.