2-μm-Compatible AlInAsSb Avalanche Photodiodes

The 2-μm optical window has recently become an area of great interest for imaging and LIDAR applications due to improved ranging capability and eye safety compared to common telecommunications wavelengths. Avalanche photodiodes (APDs) operating in this spectrum are highly desirable, as their intrinsic gain offers increased sensitivity over traditional photodiodes, further improving receiver sensitivity. HgCdTe, InAs, and InSb, as well as various superlattice materials have been used for this purpose, however, the combination of high electric field and narrow-bandgap absorber yields high dark current. As a result, these APDs are operated at cryogenic temperatures to suppress recombination mechanisms. At the high electric fields required for impact ionization, narrow bandgap materials are also susceptible to band-to-band tunneling, which cannot be suppressed by cooling. The separate absorption, charge, and multiplication (SACM) APD was designed to address this challenge by reducing the electric field in the absorber while maintaining sufficiently high enough field in the multiplication region for impact ionization [1] . This design spatially separates the absorption and multiplication layers, controlling the electric field in the absorber and multiplication layers through an intermediate charge layer. SACM APDs have been widely deployed in the InGaAs/InP and InGaAs/InAlAs materials systems for use in near-infrared telecommunications applications.