We first reported on a process for on-axis InSb crystal growth in 2014. As we have further developed on-axis (111) crystal growth, we have observed and measured a new distinct regime of interface-controlled dopant segregation. This effect is usually overshadowed by the facet effect and the resulting order of magnitude step change in the carrier concentration profile. When this large step change is eliminated, another interface-controlled effect becomes measurable. We present experimental data showing the magnitude of this effect and the crystal growth techniques used to engineer the interface where this effect is uncovered. We also discuss the atomic scale growth mechanisms that explain it.
This work proves useful in predicting the range of mechanical and electronic properties of wafers cut from ingots that are grown on-axis. More specifically, by understanding the effect of the melt/solid growth interface on the physical properties on the crystal, growth conditions can be optimized to produce more electrically uniform wafers that minimize pixel-to-pixel variation in FPAs.
CdTe and CZT materials are technologies for gamma and x-ray imaging for applications in industry, homeland security,
defense, space, medical, and astrophysics. There remain challenges in uniformity over large detector areas (50~75 mm)
due to a combination of material purity, handling, growth process, grown in defects, doping/compensation, and metal
contacts/surface states. The influence of these various factors has yet to be explored at the large substrate level required
for devices with higher resolution both spatially and spectroscopically. In this study, we looked at how the crystal
growth processes affect the size and density distributions of microscopic Te inclusion defects. We were able to grow
single crystals as large as 75 mm in diameter and spatially characterize three-dimensional defects and map the
uniformity using IR microscopy. We report on the pattern of observed defects within wafers and its relation to
instabilities at the crystal growth interface.
We present a new method to produce low-cost, high quality gallium antimonide (GaSb) substrates for IR imaging
applications. These methods apply high-volume wafer manufacturing standards from the silicon industry to increase
performance and value of our wafers. Encapsulant-free GaSb single crystals were grown using the modified Czochralski
method, yielding more than seventy 150mm wafers per crystal or several hundred 75mm or 100mm wafers per crystal.
These were processed into epi-ready substrates on which superlattice structures were grown. Wafer and epitaxy structure
characterization is also presented, including transmission X-ray topography, dopant level and uniformity.
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