Monte Carlo investigation of avalanche multiplication process in thin InP avalanche photodiodes

Abstract

An ensemble Monte Carlo simulation is presented to investigate the avalanche multiplication process in thin InP avalanche photodiodes (APDs). Analytical band structures are applied to the description of the conduction and valence band, and impact ionization is treated as an additional scattering mechanism with the Keldysh formula. Multiplication gain and excess noise factor of InP p  in  APDs are simulated and obvious excess noise reduction is found in the thinner devices. The effect of dead space on excess noise in thin APD structures is investigated by the distribution of impact ionization events within the multiplication region. It is found that the dead space can suppress the feedback ionization events resulting in a more deterministic avalanche multiplication process and reduce the excess noise in thinner APDs.avalanche photodiodes, excess noise factor, dead space, InP Avalanche photodiodes (APDs) are important components in optical receivers for the improved sensitivity provided by the internal impact ionization gain [1] . However, the available gain is limited by the excess noise due to the random fluctuation in the multiplication gain. APD noise is commonly described by the excess noise factor F. The conventional McIntyre's noise theory [2] states that the excess noise is related to the ratio between hole and electron impact ionization coefficients ,  and a low excess noise can only be achieved in materials with large difference in electron and hole coefficientsThe The McIntyre's theory has been successfully used to characterize the avalanche gain and excess noise of conventional APDs with a thick multiplication region. As the multiplication region scales down, the electric field should be increased in order to achieve the same gain. But the ratio   / in InP material tends to become unity when the applied electric field grows stronger [3,4] . Therefore, according to the McIntyre's theory, the noise performance of APDs with a thinner multiplication region will be poorer. However, recent experiments on InP and GaAs show that APDs with an ultrathin multiplication region under submicron scale demonstrate lower excess noise than that predicted by the McIntyre's theory [5][6][7] . Such facts indicate that the conventional McIntyre's theory is not applicable to thin structures because the theory is a local model which rests on the assumption that the ability of electrons and holes to impact ionize is uniform within the multiplication region and does not depend on their past history. In thin structures under submicron scale, the non-local effects such as dead space become much more significant. Dead space is the distance traveled by a carrier to gain sufficient energy from the electric field to initiate an impact ionization event. Great efforts have been made to develop theories incorporating non-local effects. Hayat et al. developed a dead space multiplication theory (DSMT) which included the dead space effect [8,9] .The DSMT model takes into account the effect of past history before a carrier can im...

First-principles calculations of electronic structure and optical properties of strained Mg2Si

“…The calculations based on the density-functional theory [8][9][10][11][12][13][14][15] and studies on the band structure have been a hot issue [12][13][14][15][16]. The first calculations of the band structures of Mg 2 Si were made in the early 1960s.…”