Current growth methods of HgCdTe/Cd(Se)Te/Si by molecular-beam epitaxy (MBE) result in a dislocation density of mid 10 6 cm À2 to low 10 7 cm À2 . Although the exact mechanism is unknown, it is well accepted that this high level of dislocation density leads to poorer long-wavelength infrared (LWIR) focal-plane array (FPA) performance, especially in terms of operability. We have conducted a detailed study of ex situ cycle annealing of HgCdTe/ Cd(Se)Te/Si material in order to reduce the total number of dislocations present in as-grown material. We have successfully and consistently shown a reduction of one half to one full order of magnitude in the number of dislocations as counted by etch pit density (EPD) methods. Additionally, we have observed a corresponding decrease in x-ray full-width at half-maximum (FWHM) of ex situ annealed HgCdTe/Si layers. Among all parameters studied, the total number of annealing cycles seems to have the greatest impact on dislocation reduction. Currently, we have obtained numerous HgCdTe/Si layers which have EPD values measuring $1 9 10 6 cm À2 after completion of thermal cycle annealing. Preliminary Hall measurements indicate that electrical characteristics of the material can be maintained.

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Silicon (211) has been proposed as an alternative substrate for CdTe/HgCdTe molecular beam epitaxial growth. Silicon has a clear advantage over other substrates because of its low cost, high strength, and thermal-expansion coefficient, which matches that of the silicon readout integrated circuit. The (211) orientation has been shown to yield high-quality CdTe and HgCdTe/CdTe layers over other orientations. The reconstruction and faceting of the Si (211) surface is poorly understood despite the importance of the (211) orientation. The results of low-energy electron diffraction (LEED) studies have been contradictory, and their conclusions are inconsistent with recent scanning tunneling microscopy (STM) studies. LEED and STM images were used to determine the most probable Si (211) surface facet structure as a function of annealing temperature. Samples annealed at a high temperature (i.e., . 1260°C) allowed the formation of ordered LEED spot patterns as opposed to the typically reported ½ 111 streaks. The pattern in the ½0 11 direction gave a consistent 23 (7.68 Å ) reconstruction.

We report on the first successful growth of the quaternary alloy Cd 1Ϫy Zn y -Se x Te 1Ϫx (211) on 3-in. Si(211) substrates using molecular beam epitaxy (MBE). The growth of CdZnSeTe was performed using a compound CdTe effusion source, a compound ZnTe source, and an elemental Se effusion source. The alloy compositions (x and y) of the Cd 1Ϫy Zn y Se x Te 1Ϫx quaternary compound were controlled through the Se/CdTe and ZnTe/CdTe flux ratios, respectively. Our results indicated that the surface morphology of CdZnSeTe improves as the Zn concentration decreases, which fits well with our previous observation that the surface morphology of CdZnTe/Si is poorer than that of CdSeTe/Si. Although the x-ray full-width at half-maximums (FWHMs) of CdZnSeTe/Si with 4% of Zn ϩ Se remain relatively constant regardless of the individual Zn and Se concentrations, etched-pit density (EPD) measurements exhibit a higher dislocation count on CdZnSeTe/Si layers with about 2% Zn and Se incorporated. The enhancement of threading dislocations in these alloys might be due to an alloy disorder effect between ZnSe and CdTe phases. Our results indicate that the CdZnSeTe/Si quaternary material with low Zn or low Se concentration (less than 1.5%) while maintaining 4% total Zn ϩ Se concentration can be used as lattice-matching composite substrates for long-wavelength infrared (LWIR) HgCdTe as an alternative for CdZnTe/Si or CdSeTe/Si.

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