Understanding ion-milling damage in epilayers
Schematic diagrams showing sample geometry: (a) MBE-grown MCT multilayer heterojunction (MLHJ) structure with interfacial superlattice (SL) layers grown on CdZnTe (211)B substrate; and (b) LPE-grown MCT double-layer heterojunction (DLHJ) structure grown on CdZnTe (111) substrate.
Transmission electron micrograph showing the cross section of MLHJ sample prepared with insufficient cooling. Note the presence of defects in LWIR, VLWIR, and SL layers, but complete absence of defects in the SWIR layer.
Cross sections of the MLHJ sample from the same wafer as sample shown in Fig. 2, but prepared at liquid nitrogen temperature. The only structural defects visible here are misfit dislocations at the SWIR/LWIR interface.
Cross-sectional electron micrographs showing the superlattice layers and VLWIR layer of the MLHJ sample prepared with sufficient cooling: (a) low magnification and (b) high magnification.
(a) Cross sections of two DLHJ epitaxial samples (different In concentrations in -type layer) prepared together, but with insufficient cooling during ion milling; (b) rethinned for with sufficient cooling; (c) rethinned for another but sample is at room temperature.
(a) Schematic diagram of ion-milling process with cooling of sample provided via thermal contact with rods from rotating sample stage to sample holder. (b) Schematic illustrating the proposed mechanism of ion-induced damage during thinning of multilayer heterojunction. Greatly enhanced diffusion into cooler zones occurs for the VLWIR layer with smaller value.
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