eSWIR and MWIR gain-based photodetectors in type-II superlattices: past, present, and future

High−speed photodetectors operating at short−wavelength infrared (SWIR) telecommunication waveband have been well studied with the development of optical fiber−based communication system. Recent innovations of photonic systems have raised new requirements on the bandwidth of photodetectors with cutoff wavelengths from extended short−wavelength infrared (eSWIR) to mid−wavelength infrared (MWIR). However, the frequency response and gain performance of photodetectors in these longer wavelength bands is less studied, and the performances of the current high-speed photodetectors in these bands are still not comparable with those in the telecommunication band. There are two major material systems are able to cover whole infrared spectrum from short− to long−wavelength infrared; HgCdTe well-developed ternary alloys and antimonide−based type−II superlattices (T2SLs). T2SLs are a developing new material system with intrinsic advantages such as great flexibility in bandgap engineering, low growth and manufacturing cost, high−uniformity, auger recombination suppression, and high carrier effective mass that are becoming an attractive candidate for infrared detection and imaging. Thanks to T2SLs' extreme design flexibility one can demonstrate many different device architectures that could not been realized in other material systems to achieve higher gain and speed such as hetero−junction phototransistor (HPT) and avalanche photodiodes (APD) with bandstructure−engineered multiplication regions. We are going to present an overview of eSWIR and MWIR gain−based devices (such as HPTs and APDs) in T2SLs material system and possible routes to achieve higher gain and faster speed in these devices.