Design And Simulation Of The Mg₂Si/Si Heterojunction Photodiode

In order to develop infrared detectors base on Mg₂Si thin films which are environmentally friendly materials,focusing on the Mg₂Si/Si heterojunction photodiodes,Mg₂Si/Si heterojunction photodiode detectors with different structures were designed and simulated by using Silvaco and wx AMPS software after the physical parameters of Mg₂Si and Si materials were selected and the device models of the Mg₂Si/Si heterojunction photodiodes were established.First,the spectral responses of the pn-type and pin-type Mg₂Si/Si heterojunction photodetectors were simulated and analyzed.The simulation results show that the Mg₂Si photosensitive layer has a greater impact on device performance.Increasing the thickness of the photosensitive layer and reducing the doping concentration are effective ways to improve the spectral response.However,when the doping concentration is below 1x10¹⁶cm^-3,the dark current will be greatly improved.When the thickness of the Mg₂Si photosensitive layer is 4?m,The Mg₂Si/Si pin heterojunction photodiode is more sensitive in the spectral range of 0.6?1.5?m than Mg₂Si/Si pn heterojunction photodiode.The peak wavelength of the photodiode is1.11?m and the maximum responsivity of 0.742 AW^-1.The wavelength of 1.31?m still has a good responsibility of up to 0.53 A.W^-1.Dark current density of the pin photodiode is approximately 1×10^-6 A.cm^-2,which is slight bigger than that of the pn photodiode.The back irradiation has higher quantum efficiency than the front irradiation when short-wave light illuminates the device,and it is almost coincide when long-wave light is irradiated to the device.The switching characteristics of pin photodiode device are slightly reduced than that of the pn photodiode,both of which have high switching speeds in the nanosecond range.Therefore,the Mg₂Si/Si pin heterojunction structure is better than the pn heterojunction structure.At the same time,the performance of the p-Si/i-Mg₂Si/n-Si type is not much higher than that of the p-Mg₂Si/i-Mg₂Si/n-Si type photodiode.Considering the influence of the interface state of Mg₂Si/Si heterojunction,the p-Mg₂Si/i-Mg₂Si/n-Si type structure is a better choice.Then,the Mg₂Si/Si avalanche photodiode was simulated and analyzed.The separate absorption,charge and multiplication avalanche photodiode?SACM-APD?with the Mg₂Si absorption layer was constructed by using the Atlas module.The internal electric field strength and I-V characteristics of Mg₂Si/Si APD were preliminary simulated,and the effects of structural parameters of device,such as the charge layer and the multiplier layer on the penetration voltage and the breakdown voltage were studied.The simulation results show that the Mg₂Si films as absorption layer can effectively extend the spectral response range of silicon avalanche photodiodes.The thin and low-doped charge layer will cause the absorption layer of device to be exhausted with the small bias,and the device is punched in advance.However,the larger bias is required to cause the device to break down and cause the effect of dead space.The thicker and highly doped charge layer will reduce the difference??V_b-V_p?between the breakdown voltage and the penetration voltage of the device even if the device has been broken down when the depletion layer is not completely depleted.As the thickness of the multiplying layer w_m increases,the breakdown voltage of the device firstly decreases and then increases.At 0.6?m,the breakdown voltage has a minimum value(1_?78?49))of 53 V,and the penetration voltage increases linearly.The doping concentration in the multiplication layer d has little effect on the breakdown voltage,but when the doping concentration is greater than 1x10¹⁵cm^-3,the electric field distribution of the multiplier layer shows a large degree of tilt,which will generate a high dark current.Increasing the bias voltage and the thickness of the multiplication layer reduce the device capacitance.Increasing the bias voltage and the thickness of the multiplication layer will reduce the capacitance density of the device.In addition,the thickness of the multiplier layer has little effect on the transient response of the device.According to the simulation calculations,the gain coefficient and the quantum efficiency of light absorption of SACM-APD after preliminary optimization were given.When the incident light wavelength is 1.31?m and the optical power is 10 m W/cm²,the breakthrough voltage and the penetration voltage of the designed avalanche photodiode are 50 V and 17.5 V.When the bias voltage is 47.5V?0.95V_b?,and the incident light wavelength is 1.1?m,the peak value of the spectral response is 25 AW^-1,the dark current is about 1.8x10^-9A,the multiplication factor is 19.6,and the maximum value of the device at is 102 when the device is broken down.The average magnification M of the device current is 75.4,and the effect on the current gain is better.The three types of Mg₂Si/Si heterostructure photodetectors were designed and simulated.The simulation results show that the SACM-APD structure can be used to obtain a high-performance infrared detector based on Mg₂Si thin film.