Expanding the Vision of Sensor Materials (1995) / Chapter Skim
Currently Skimming:
CHAPTER 5: LWIR SENSORS
CHAPTER 5: LWIR SENSORS
Pages 62-72
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 62... ...
The Department of Defense has made substantial investments in materials research for applications in LWIR sensors, due 62 to DoD requirements for reconnaissance and night vision capabilities. For example, the military has a need to track large numbers of ballistic missiles and their associated warheads; this dictates requirements for very discriminating sensors.
|
From page 63... ...
Given that no binary material is suitable for use as an LWIR detector material, different strategies have been used to obtain a material with the "right" bandgap. Three such materials strategies for obtaining high-efficiency infrared detectors are discussed below: MCT (mercury-cadmium-telluride)
|
From page 64... ...
As mentioned previously, there are at least three materials strategies for producing LWIR sensors and each is at a different level of maturity. Currently, the performance of LWIR sensors imple
|
From page 65... ...
Materials quality has improved over the last decade, and continued incremental improvements may eventually yield temporally stable, uniform detector arrays for LWIR applications. However, at the present time, major materials and processing challenges remain.
|
From page 66... ...
art go- 0~ (D ~ o =e (D o- ~ ~ ~ ~ ~ ~ C A 5t I
|
From page 67... ...
LWIR Detectors Based on Strained-Layer Superlattice Structures Desired band gaps for LWIR detection can be artificially created in semiconductor heterostructures by employing lattice strain to cause major changes in electronic and optical properties of the material. Significant materials and processing issues are involved in the growth and processing of strainedlayer superIattice (SLS)
|
From page 68... ...
Growth of bulk alloys on a substrate with a sigIiificantly different lattice constant leads to high dislocation densities and microcracks which severely limit the device performance. Even if high-performance devices could be developed in these bulk alloys, the cutoff wavelength would be limited to less than 9-pm at 77 K
|
From page 69... ...
Decoupling the band gap and the effective mass eliminates the limiting feature of bulk alloy systems for very long wavelength operation. High-quality InSb/InAsSb SLSs have been grown both by molecular beam epitaxy and metalorganic chemical vapor deposition (Dawson, 1989; Biefeld, 1986~.
|
From page 70... ...
MCT The quality of LWIR MCT has improved over the last decade, and continued incremental improvements may eventually yield temporally stable, uniform detector arrays for LWIR applications. However, materials instabilities result in major materials and growth challenges.
|
From page 71... ...
Currently, individual gallium-arsinide-AIGaAs heterostructure detectors have a specific defectivity of about one-third that of the fundamental limit. Because of superior response uniformity, arrays of these structures already exhibit performance exceeding that of MCT detector arrays for selected applications despite the higher theoretical detectivity of mercury-cadmium-telluride.
|
From page 72... ...
=1.0x10~° cm-Hzi/2/W GaAs AlGaAs multiquantum well Lambda=8.3 mu-m infrared detector. Applied Physics Letters 53~4~:296.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.