Dual-band infrared detectors

As the infrared technology continues to advance, there is a growing demand for multispectral detectors for advanced IR systems with better target disc rimination and identification. Both HgCdTe detectors and quantum well GaAs/ AlGaAs photodetectors offer wavelength flexibility from medium wavelength t o very long wavelength and multicolor capability in these regions. The main challenges facing all multicolor devices are more complicated device struc ttures, thicker and multilayer material growth, and more difficult device f abrication, especially when the array size gets larger and pixel size gets smaller. In the paper recent progress in development of two-color HgCdTe ph otodiodes and quantum well infrared photodetectors is presented. More attention is devoted to HgCdTe detectors. The two-color detector array s are based upon an n-P-N (the capital letters mean the materials with larg er bandgap energy) HgCdTe triple layer heterojunction design. Vertically st acking the two p-n junctions permits incorporation of both detectros into a single pixel. Both sequential mode and simultaneous mode detectors are fab ricated. The mode of detection is determined by the fabrication process of the multilayer materials. Also the performances of stacked multicolor QWIPs detectors are presented. For multicolor arrays, QWIP's narrow band spectrum is an advantage, resulti ng in low spectral crosstalk. The major challenge for QWIP is developing br oadband or multicolor optical coupling structures that permit efficient abs orption of all required spectral bands.