Research Review: Antimonides Aid Infrared Detection
RESEARCHERS at the University of Virginia are developing incredibly versatile, infrared photodetectors based on quantum wells made from InGaAs and GaAsSb.
These devices operate at room temperature and span the spectral range from 800 nm to 2.8 μm, making them suitable for a wide variety of applications that include telecommunications, night vision, tumor sensing and gas monitoring and detection.“There are other detectors that can detect fairly well in this wavelength regime but they either need cooling or have a low fabrication yield", says Jinrong Yuan.
Yuan points out that one interesting and beneficial feature of the InGaAs/GaAsSb system is its type II structure, which dictates that optical transitions are indirect and occur between adjacent layers. The effective bandgap is consequently narrower than bulk InGaAs, enabling detection at longer wavelengths.
It is possible to stretch the detection of bulk InGaAs to 2.5 μm by straining the ternary layer, but this step introduces defects, increases dark current, and ultimately demands detector cooling. The type II structures pioneered by researchers at the University of Virginia, however, are lattice-matched.
This team has recently fabricated detectors with an absorption region made from 100 alternating layers of 7 nm-thick In0.53Ga0.47As and 5-nm thick Ga0.5As0.5Sb.
Performance of this MBE-grown device has been compared to that of a conventional InGaAs detector, which was also made by the researchers. Dark current in the type II detector is more than two orders of magnitude higher due to defects at the interfaces in the quantum well region and a higher density of thermal carriers, which results from the smaller effective bandgap.
Measurements by the engineers revealed that the efficiency of the more novel detector exceeded that of its bulk cousin, delivering quantum efficiencies of 80.2 percent and 57.8 percent at 1064 nm and 1550 nm, respectively.
The team’s next goal is to improve the quantum efficiency of its device over its entire range of 800 nm to 2.8 μm.
J. Yuan et al. Electron. Lett 47 1144 (2011)