Electron avalanche photodiodes (e-APDs) are a new class of avalanche photodiode in which multiplication occurs entirely from the impact ionization of electrons. Theoretically, the maximum impulse response duration for an e-APD—equal to the sum of the electron and hole transit times across the multiplication region—remains constant regardless of its operational gain, meaning that e-APDs (unlike conventional APDs) should not be restricted by a gain-bandwidth product limit. These e-APDs have recently been demonstrated for II-VI and III-V material systems using mercury cadmium telluride (HgCdTe) and indium arsenide (InAs); however, the bandwidth of HgCdTe devices is limited to hundreds of megahertz and their low bandgap energy necessitates operation at 77 K.
By exploiting the fundamental properties of e-APDs and recent advances in InAs diode fabrication, researchers at Lancaster University (Lancaster, England) and the University of Sheffield (Sheffield, England) have made the first high-bandwidth, waveguide-coupled InAs e-APDs. The multiplication region width w has been optimized for both high bandwidth and high gain, leading to the demonstration of room-temperature-operation n-i-p type e-APDs with a 430 GHz gain-bandwidth product, as well as 580 GHz e-APDs operating at 77 K. This paves the way for future e-APDs that can achieve the terahertz gain-bandwidth products needed for next-generation communications and other high-speed detection applications. Contact Andrew Marshall at [email protected].
