L. O. Bubulac

Impact of Tellurium Precipitates in CdZnTe Substrates on MBE HgCdTe Deposition

State-of-the-art (112)B CdZnTe substrates were examined for near-surface tellurium precipitate-related defects. The Te precipitate density was observed to be fairly uniform throughout the bulk of the wafer, including the near-surface region. After a molecular beam epitaxy (MBE) preparation etch, exposed Te precipitates, small pits, and bumps on the (112)B surface of the CdZnTe wafer were observed. From near-infrared and dark field microscopy, the bumps and small pits on the CdZnTe surface are associated with strings of Te precipitates. Raised bumps are Te precipitates near the surface of the (112)B CdZnTe where the MBE preparation etch has not yet exposed the Te precipitate(s). An exposed Te precipitate sticking above the etched CdZnTe surface plane occurs when the MBE preparation etch rapidly undercuts a Te precipitate. Shallow surface pits are formed when the Te precipitate is completely undercut from the surrounding (112)B surface plane. The Te precipitate that was previously located at the center of the pit is liberated by the MBE preparation etch process.

Impurity Gettering in (112)B HgCdTe/CdTe/Alternate Substrates

The crystalline structure and impurity profiles of HgCdTe/CdTe/alternate substrate (AS; Si and GaAs are possibilities) and CdTe/AS were analyzed by secondary-ion mass spectrometry, atomic force microscopy, etch pit density analysis, and scanning transmission electron microscopy. Impurities (Li, Na, and K) were shown to getter in as-grown CdTe/Si epilayers at in situ Te-stabilized thermal anneal (~500°C) interfaces. In HgCdTe/CdTe/Si epilayers, indium accumulation was observed at Te-stabilized thermal anneal interfaces. Impurity accumulation was measured at HgCdTe/CdTe and CdTe/ZnTe interfaces. Processing anneals were found to nearly eliminate the gettering effect at the in situ Te-stabilized thermal anneal interfaces. Impurities were found to redistribute to the front HgCdTe/CdTe/Si surface and p–n junction interfaces during annealing steps. We also investigated altering the in situ Te-stabilized thermal anneal process to enhance the gettering effect.