A new look at impact ionization-Part II: Gain and noise in short avalanche photodiodes

Abstract

In Part I, a new theory for impact ionization that utilizes history-dependent ionization coefficients to account for the nonlocal nature of the ionization process has been described. In this paper, we will review this theory and extend it with the assumptions that are implicitly used in both the local-field theory in which the ionization coefficients are functions only of the local electric field and the new one. A systematic study of the noise characteristics of GaAs homojunction avalanche photodiodes with different multiplication layer thicknesses is also presented. It is demonstrated that there is a definite "size effect" for thin multiplication regions that is not well characterized by the local-field model. The new theory, on the other hand, provides very good fits to the measured gain and noise. The new ionization coefficient model has also been validated by Monte Carlo simulations.

Germanium avalanche receiver for low power interconnects

“…The multiplication process is initiated by electrons and holes, and both are multiplied within the intrinsic region. According to the impact ionization theory [21][22][23][24] , a high excess noise factor should then be obtained as electrons and holes have quite similar impact ionization coefficients in Ge 25 . However, a narrow width multiplication region (500 nm) was chosen in the design to promote a large dead space effect 23,26 contribution favouring an efficient reduction of the excess noise factor.…”

Numerical Analysis of Homojunction Avalanche Photodiodes (Apds)

“…The origin is at the interface of the n and i regions, and the thickness of the i region is ω. Thus, electrons are swept to the left and holes to the right [30].…”

“…The ionization probability of this electron p e (x |x) in dx thus depends on the electron survival rate P se (x |x). The survival rate and ionization probability of holes are defined similarly [30].…”

“…The multiplication noise is described in terms of the current noise power spectral density. According to the local-field theory, the noise power spectral density s(x) of a δ pair injection at x is [30] s…”

“…With the assumption that β = kα and only electrons are injected at x = ω, boundary condition is given by: [30] …”