Auger Excitation Shows APD-like Gains

A group of UCSD researchers publishes an open-access Applied Physics Letters paper "An amorphous silicon photodiode with 2 THz gain‐bandwidth product based on cycling excitation process" by Lujiang Yan, Yugang Yu, Alex Ce Zhang, David Hall, Iftikhar Ahmad Niaz, Mohammad Abu Raihan Miah, Yu-Hsin Liu, and Yu-Hwa Lo. The paper proposes APD-magnitude gain mechanism in by means of 30nm-thing amorphous Si film deposited on top of the bulk silicon:

"APDs have relatively high excess noise, a limited gain-bandwidth product, and high operation voltage, presenting a need for alternative signal amplification mechanisms of superior properties. As an amplification mechanism, the cycling excitation process (CEP) was recently reported in a silicon p-n junction with subtle control and balance of the impurity levels and profiles. Realizing that CEP effect depends on Auger excitation involving localized states, we made the counter intuitive hypothesis that disordered materials, such as amorphous silicon, with their abundant localized states, can produce strong CEP effects with high gain and speed at low noise, despite their extremely low mobility and large number of defects. Here, we demonstrate an amorphous silicon low noise photodiode with gain-bandwidth product of over 2 THz, based on a very simple structure."