Structural and chemical disorder in semiconductors under pressure: Evidence in II-VI's, role of photoactive defects, material predictions

Hydrostatic pressure can sometimes generate structural and chemical disorder within crystals. We review pressure-Raman experiments on ZnSe, ZnTe, and CdSe showing evidence for these phenomena. In ZnSe and ZnTe Raman spectra recorded with low laser flux show only pre-transition structural disorder on approaching the lowest pressure transition, as is typical for first-order phase changes. Spectra recorded with higher laser flux (sub-band-gap) observe precipitation of anion nanocrystals. This behavior is absent in CdSe. A model is developed that considers the role of crystal defects. The defects promote plastic deformation assisted by photoexcitation of Jahn-Teller distortions. Nanocrystals can precipitate on dislocations in deformed regions under energetically favorable conditions. Model calculations based on theories for precipitation in metals account for the influence of pressure on the nanocrystal formation in ZnSe and ZnTe, and explain its absence in CdSe. Material maps are constructed to predict the tendencies for similar precipitation in III-V, II-VI, I-VII, and chalcopyrite crystals.