Molecular beam epitaxial growth of HgCdTe mid-wave infrared dual-band detectors

The technique of molecular beam epitaxy (MBE) has been utilized to fabricate high-performance HgCdTe infrared detectors, which exhibit sensitivity to mid-wave infrared radiation in adjacent spectral bands for twocolor thermal imaging applications. The growth of a multilayer HgCdTe device structure by MBE enables the use of an n-p-n device architecture, which facilitates pixel-level registration of images in two separate spectral bands. Device structures are grown on CdZnTe (211)B substrates using CdTe, Te, and Hg sources with in situ indium (In) and arsenic (As) doping. The composition of the HgCdTe alloy layers is adjusted to achieve detection of infrared radiation in adjacent spectral bands within the wavelength range of 3.0-5.0 mu m. The as-grown device structures are characterized using X-ray diffraction, wet chemical defect etching, and secondary ion mass spectrometry. The 640 x 512, 20-mu m-pixel-pitch dual-band MWIR1/MWIR2 focal-plane arrays (FPAs) are fabricated by mesa etching, sidewall passivation and other processes. Ohmic contacts are made to the two n-type layers for operation of the detectors in a sequential detection mode. The MWIR1/MWIR2 FPAs, which are fabricated using these HgCdTe heterostructures with exceptionally high-quality layers, exhibit a band 1 (MWIR1) operability of 98.65 % and a band 2 (MWIR2) operability of 99.93 %. The NETD values of both MWIR1 and MWIR2 modes are less than 15 mK.