Cascaded homojunction avalanche photodiodes

Abstract

The structure and the performance of a cascaded avalanche photodiode (APD) based on cascaded homojunctions are discussed. Similar to the hetero-structure superlattice APD, such a device has a lower excess noise and a higher gain at lower bias voltages than conventional APDs. In addition to the ionization ratio, several parameters also affect the device's performance.

High-gain high-speed low-noise single-avalanche-stage APDs

“…It is not hard to understand from the figures that the noise is smaller than what the conventional McIntyre predicted when the N is finite and small. For the N=1 case, the excess noise factor is always smaller than 2 and the highest gain can be obtained from such a case is when the k-ratio is approaching to I [10]. Such an N=1 device has been named as the "ballistic avalanche photodiode" and expected to be able to produce ultra-low noise APDs [15].…”

“…N is the number of ionizing collisions per carrier transit, Me i5 the total gain of the N ionization stage and g, g represent the electron and hole gain per ionization stage [9,10]. Fig.…”

“…On the contrary, in many state-of-the-art devices the number N of possible ionizations is finite and perhaps even very small (N=1-5). The smaller the multiplication region, the smaller the number impact ionization will happen and smaller the APD noise will be [9,10]. Indeed, Campbell et al have observed SAM (separate absorption and multiplication) -APDs with lower multiplication noise than predicted by conventional continuum noise theory when they reduce the multiplication layer thickness from I 500 nm to less than 500 nm [I 1,12].…”