This article reports a multi-gain-stage avalanche photodiode based on InGaAs/InAlAs superlattice, which has much higher gain and signal-to-noise ratio than conventional APD. The physical mechanism of high gain and low noise of this type of APD is analyzed in detail, and the dead space gain theory (DSMT) is introduced and applied to the calculation of the excess noise factor of multi-gain-stage APD. For a 5-stage device, the distribution of electric field and carrier dead space is calculated, and the ionization rates before and after considering phonon scattering are compared. The gain vs excess noise factor curve is obtained and compared with the traditional McIntyre model. The simulation results shows that the excess noise factor is equivalent to the McIntyre model k=0.049. Based on the simulation results, an optimized epitaxial material structure is designed, Front-illuminated photo diode were etched in the molecular beam epitaxy (MBE)-grown epitaxial material, the mesa sidewalls were encapsulated with Si3N4 . The test results of a 50μm diameter device are as follows: maximum above 1000, excess noise factor of 2.39@M=100, spectral response range of 0.95~1.65μm, response time of 1.26ns.
Impact ionization in charge layer and multiplication layer of InAlAs/InGaAs avalanche photodiodes (APDs) with separated absorption, grading, charge and multiplication structures has been studied by two-dimensional simulations using Silvaco TCAD. Special attention has been paid to the charge layer and multiplication layer with different thicknesses and doping concentrations in order to optimize the structure for low band discontinuities and an appropriate electric field distribution. Band-edge profile calculations as well as current–voltage characteristic and electric field results of the APDs will be discussed in this article.
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