Dr. Sarath Gunapala
The most common infrared detectors are based on the principle of interband absorption in narrow bandgap II-VI semiconductors. However, such narrow bandgap II-VI materials are more difficult to grow and process into devices, reducing the yield and increasing the cost of the arrays. These difficulties motivate the exploration of artificial low effective bandgap structures built from wide bandgap III-V semiconductors such as GaAs, InP, GaSb, which, are far easier to grow and process into devices. Thus, Jet Propulsion Laboratory is developing III-V materials based quantum well infrared photodetectors (QWIPs), quantum dot infrared photodetectors (QDIPs), and Strain Layer Superlattice (SLS) based detectors for infrared detection applications.
Arguably one of the simplest device realizations of the classic particle-in-a-box problem of basic quantum mechanics is the QWIP. Optimization of the detector design and material growth and processing has culminated in the realization of portable long-wavelength infrared cameras with a large focal plane arrays (FPAs).
We have used molecular beam epitaxy (MBE) technology to grow multi-layer quantum dot structures based on the InAs/InGaAs/GaAs material system. Recently, we have fabricated the first long-wavelength 640x512 pixels QDIP FPA and this FPA produced excellent infrared imagery. Furthermore, we report on the status of FPAs based on GaSb/InAs type-II SLS diodes grown by molecular beam epitaxy (MBE) and designed for infrared absorption in the 2-5µm and 8-10µm bands.