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Jacobs R.N.,U.S. Army | Benson J.D.,U.S. Army | Stoltz A.J.,U.S. Army | Almeida L.A.,U.S. Army | And 4 more authors.
Journal of Crystal Growth | Year: 2013

High threading dislocation densities limit the operability of infrared focal plane arrays based on large lattice-mismatched heterostructures such as HgCdTe/CdTe/Si. Recently it has been shown that postgrowth thermal cycle annealing can routinely reduce the surface etch pit density from <5 × 106 cm-2 to as low as 9 × 105 cm -2. To fully exploit the procedure, a deeper understanding of the inherent dislocation dynamics is needed. In this work, we employ scanning transmission electron microscopy to analyze cross-sectional samples of HgCdTe/CdTe/Si prepared using site-specific focused ion beam milling. A key factor in this work is the use of defect decorated samples, which has allowed for a correlation of surface etch pits to dislocation segments observed in cross-section images. We have observed that the previously reported oval-shaped etch pits are likely associated with Shockley partial type dislocations, and that triangular etch pits are associated with perfect dislocations. This suggests the likelihood that interaction between mobile Shockley partial and other dislocation types are responsible in part for the observed reduction in top surface etch pit density. These studies provide a deeper understanding of dislocation reduction processes which are critical for the realization of high performance infrared detectors based on low-cost, lattice-mismatched substrates. Source

Jacobs R.N.,U.S. Army | Stoltz A.J.,U.S. Army | Benson J.D.,U.S. Army | Smith P.,U.S. Army | And 8 more authors.
Journal of Electronic Materials | Year: 2013

Due to its strong infrared absorption and variable band-gap, HgCdTe is the ideal detector material for high-performance infrared focal-plane arrays (IRFPAs). Next-generation IRFPAs will utilize dual-color high-definition formats on large-area substrates such as Si or GaAs. However, heteroepitaxial growth on these substrates is plagued by high densities of lattice-mismatch-induced threading dislocations (TDs) that ultimately reduce IRFPA operability. Previously we demonstrated a postgrowth technique with the potential to eliminate or move TDs such that they have less impact on detector operability. In this technique, highly reticulated mesa structures are produced in as-grown HgCdTe epilayers, then subjected to thermal cycle annealing. To fully exploit this technique, better understanding of the inherent mechanism is required. In this work, we employ scanning transmission electron microscopy (STEM) analysis of HgCdTe/CdTe/Si(211) samples prepared by focused ion beam milling. A key factor is the use of defect-decorated samples, which allows for a correlation of etch pits observed on the surface with underlying dislocation segments viewed in cross-section STEM images. We perform an analysis of these dislocations in terms of the general distribution, density, mobility at various locations within the mesa structures. Based on our observations, we suggest factors that contribute to the underlying mechanism for dislocation gettering. © 2013 TMS (outside the USA). Source

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