This paper describes some recent results on surface defects, uniformity, dislocation density as well as device applications of MBE growth of HgCdTe at the research center of advanced materials and devices. The features of different surface defects and their origins were studied by using SEM/EDX observations on HgCdTe epilayers with different growth conditions. A variety of surface defects was observed and the formation mechanism was discussed. A good uniformity was observed over 3-in HgCdTe wafers, the Stddev/mean in x and thickness were 1.2%, and 2.7%, respectively. It was found that the dislocation density was sensitive to growth parameters and the composition. The ZnCdTe substrates with 4% mole fraction were found to be suitable for LW HgCdTe, however, for the HgCdTe of shorter wavelengths different Zn composition is required. An average value of EPD of 4.2×105cm−2 was obtained for LW samples. The MBE grown HgCdTe were incorporated into some preliminary FPA devices.
The recent progress in MBE growth of HgCdTe at the Research Center for Advanced Materials and Devices, and the National Laboratory for Infrared Physics is reported. It is found that the excellent compositional uniformity and reproducibility of HgCdTe can be archived by MBE technique. The results of surface morphology, dislocation density, electrical properties and focal plane array detectors are described in the paper.
Some newly obtained photoluminescence (PL) data from the ZnSe:Cl epilayers grown by molecular beam epitaxy are reported here. The PL spectrum at 10 K is dominated by a strong and narrow Cl0X peak at 2.797 eV with the FWHM of about 13 meV. The quenching tendency of Cl0X peak with the increasing temperature is clearly characterized by two temperature regimes, corresponding to two thermal activated nonradiative mechanisms with activation energies of about 16 meV and 90 meV respectively. The weak emission at 2.713 eV is thermally quenched by the presence of nonradiative center with the same activation energy of about 90 meV as the Cl0X. The similar quenching tendency of the 2.713 eV emission and the Cl0X peak implies that they are quenched by the same physical mechanisms.
The recent progress in MBE growth of HgCdTe at the Epitaxy Research Center for Advanced Materials, and the National Laboratory for Infrared Physics is described. It was found that the surface morphology is sensitive to the growth temperature and the flux ratio. The compositional reproducibility studied in a limited number of samples showed that a STDDEV for x-values of 0.0017 deviated from an average value of 0.229 was obtained. The epilayers showed excellent compositional uniformity across 2-inch wafers, the relative deviations for x-value and thickness were found to be 0.18 percent and 2.19 percent respectively. Ellipsometer was used for real-time monitoring the compositional variations during growth. The post growth annealing process was found to be effective in reducing the dislocation density, a reduction in dislocation density by approximately 50 percent could be obtained even by approximately 250 degrees C low temperature annealing. Electrical properties of epilayers are described, and a p-type in situ vacuum annealing process was demonstrated. MBE grown p-HgCdTe epilayers were successfully incorporated into 32 X 32 focal plane arrays detectors.
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