Dislocation Reduction of HgCdTe/Si Through Ex Situ Annealing

Abstract

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.

Effect of Cycle Annealing Parameters on Dislocation Density Reduction for HgCdTe on Si

“…10,11 The temperatures reported in previous works were in reference to the set-point of the furnace, as an accurate temperature calibration was not known at the time. Since the publication of those articles, the actual sample temperature has been calibrated from the furnace set-points, as explained in the ''Experimental Procedures'' section.…”

“…We previously reported that, for temperatures greater than 500°C, the EPD reduces to 1 9 10 6 cm À2 after four or more cycles. 10,11 Closer inspection of TCA performed at 550°C revealed that EPD saturation can be expected after two or three cycles of annealing. At a lower temperature of $450°C we find that it requires 16 cycles to reduce the EPD to the 1 9 10 6 cm À2 level.…”

“…[6][7][8][9][10][11] Previous work has mainly focused on the extent to which dislocation density can be reduced via TCA. Using TCA, an etch pit density (EPD) saturation limit of $1 9 10 6 cm À2 can be consistently achieved by applying appropriate annealing conditions.…”

“…It has been shown that the saturation limit can be achieved regardless of the HgCdTe layer as-grown EPD or buffer layer EPD. 10,11 In this paper, we examine the effect of temperature and number of TCA cycles on dislocation densities, both at the surface and throughout the bulk of the crystal.…”

Study of HgCdSe Material Grown by Molecular Beam Epitaxy

“…1 It has been demonstrated that this higher dislocation level results in lower device performance, especially in the LWIR regime. 2 There is ongoing effort within the community to either reduce dislocations in HgCdTe/Si or render the dislocations electrically inactive, [3][4][5][6] but to date no single approach yields material with dislocation density values or device performance similar to those of HgCdTe grown on bulk lattice-matched substrates. Without use of scalable and relatively inexpensive substrates, the development of third-generation IRFPAs using Hg-based compounds is severely hindered as large format sizes and cost are major drivers for future systems.…”