Antimonide-based type-II quantum well infrared photodetectors

To enhance the performance of mid-to-far infrared (MIR to FIR) photodetectors towards room temperature operation is an ongoing quest. Motivated by this challenge, this work started with studying the carrier transport properties of InAs/InGaSb type-II superlattice (T2SL) photodiodes followed by investigations on surface passivation schemes to improve their performance at 78 K and above. Eventually this leads to the discovery of interband cascade detectors (ICDs) capable of photovoltaic operation at room temperature. After fabrication and characterization of T2SL photodiodes, the electron beam induced current (EBIC) technique was used to quantitatively extract the electron minority lifetime and diffusion length to study their dependences on temperature and interface conditions. The physicochemical mechanisms of ammonium sulfide surface passivation on InGaAsSb, a pilot material for T2SL due to their chemical similarity, were analyzed using x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) techniques. The ammonium sulfide passivation effectively reduces the dark current of InGaAsSb photodiodes and its long-term stability is enhanced by combination with polyimide encapsulation. Similar passivation schemes were applied to T2SL photodiodes to achieve surface recombination velocity reduction (>100 times), dark current reduction (4 times), and an increase in dynamic resistance area product (R0A) by 74%. On the other hand, EBIC and near-field light-beam-induced current (LBIC) experiments of interband cascade lasers revealed superb transport and collection efficiency for electron-beam-induced or photo-excited carriers at room temperature. Ensuing fabrication and characterization of photodetectors from such structure resulted in the discovery of interband cascade detectors (ICDs) with encouraging detectivity (1.4 x 109 cmHz1/2/W) and R 0A (19 Ocm2) under zero bias at room temperature. In an ICD, the electrons and holes generated from interband optical transitions (time constant ∼ nanoseconds) are efficiently separated and collected, respectively, via the much faster (typically <100 ps) intersubband relaxation and interband tunneling processes, which promises ICDs of potentially high performance at high temperature. In a bias electric field, the linear and bipolar Stark effects (∼1 meV shift per 10 kV/cm) of the type-II quantum well in the interband cascade structure were studied, with potential applications in integrated optoelectronic devices such as voltage tunable photodetectors, optical modulators, and wavelength converters.