Study Of The Novel Mesa Structure Avalanche Photodiode Based On Silicon

With the development of optical communication technology and theimprovement of social information-based degree, the application of low-lightdetection technology more widely.with the advantages of high quantum efficiency,small size, insensitivity to magnetic fields, low operating voltage and working at roomtemperature, avalanche photodiode (APD) has become a hot topic in the field oflow-light detection. Due to Si material have the characteristic of low carriers impactionization rate ratio, little tunneling current, making Si APD high gain, low noise andstability well, and has a wide range of application in the wavelength range of400nm~1100nm. In this paper, we propose a novel mesa Si APD structure which hasa high internal gain and low breakdown voltage. In order to analysis the performanceof the device, we design the equivalent circuit mode for Si APD. Combine withsimulation, we designed a high internal gain and low breakdown voltage APDphysical structure, and studied the relationship of multiplication region doping,floating layer doping and mesa size with APD’s performance. The main contents ofthis dissertation were organized as following:(1) Design of Si APD equivalent circuit modelFirst, the distribution of internal electric field for SCAM APD structure wasanalyzed theoretically, and then through the carrier density rate equation and photondensity rate equation, Si APD equation equivalent circuit mode was designed. Next,the relationship of avalanche multiplication layer thickness and the breakdownvoltage, the absorption layer thickness with response speed were discussed. Theresults show that: with the multiplication layer thickness reduces, the internal electricfield increases, but the avalanche breakdown voltage is gradually decreased; whenabsorption layer thickness is reduced, the carriers have a fast transit speed, lead to theimprove of APD response speed, but it also reduce the light-generated current andquantum efficiency.(2)Design and simulation of novel Si APD structurea) The influences of doping dose of multiplication region on breakdown voltageand spectral response were analyzed. The simulation result showed that thebreakdown voltage of the Si APD quickly rose from16.3V to203V and the peakresponse wavelength from480nm red shift to800nm, corresponding peak responsibility increase from11.2A/W to372.3A/W close to breakdown voltage, whenthe boron implantation dose in the multiplication region decreases from5.0×1012cm-2to2.5×1012cm-2.b) A internal electric field was built between floating layer and P+charge layer,and the electric field reduces the electric field in stepped side walls, so that thephoto-generated carriers transit to the direction which close to the center area, caneffectively inhibit the avalanche multiplication near the stepped side walls, lead to thereduce of surface dark current and the increase of gain in device, and which alsoimprove the stability and reliability of the device. The simulated result show that: asfloating ring implantation dose was increased from0to1×1011cm-2, Si APD’s gainwas increased from5×103to2.5×104abruptly.c) The barrier height in the bottom of mesa is related with the mesa size of Si APD.The reduction of mesa size makes the barrier increase, benefit to photo-generatedcarriers’ transit to the center mesa region. While the reduction of mesa size, the darkcurrent also decreases linearly, which lead to the increase of the gain. The simulationshowed that when mesa size was reduced from10μm to0.1μm, the gain increasedfrom104to106exponentially, and the breakdown voltage was also graduallyincreased due to the resistance in the mesa region increase.(3) Simulation of key fabrication processThe doping progress of Si APD was used by ion implantation, and we study theinfluence of implantation conditions and thermal annealing with the distribution ofdoping. Simulation studies found that with increasing annealing time, the phosphorusimpurities spread gradually, making the width of multiplication layer decreases,which resulting avalanche breakdown voltage decrease. As well, through transmissionspectrum of Si material, if the rapid thermal annealing time too long will cause thespread of high density defects, which was disadvantage for the preparation of thedevice.