Ph.D Thesis


Ph.D StudentSharon Shwartz
SubjectNonlinear Optics in CdZnTe:V
DepartmentDepartment of Physics
Supervisor Full Professors Segev Mordechai
Full Thesis textFull thesis text - English Version


Abstract

This dissertation deals with the enormous change in the optical and electrical properties of the bulk semiconductor crystals CdZnTe:V (CZT:V) driven by light illumination at moderate intensity and moderate applied electric field. All these phenomena were discovered during my PhD research. My research was aimed to explore the physical origins of these phenomena and demonstrate new applications, primarily in the field of nonlinear optics. The main results of my doctoral research as described in this thesis, are as follows.


  •                   Light-induced large enhancement of electro-opticand electrostriction effects in CZT:V
    We observed light-induced reversible strain effects in CdZnTe:V crystals, leading to a remarkable enhancement of their nonlinear properties, such as electrostriction and electro-optic effects. We measured light-induced relative deformation of the initial crystalline lattice up to 0.15%. We measured refractive index changes which exceed the large value of 0.01. These are the largest electro-optic and electrostriction effects ever demonstrated in any inorganic bulk material.

  •                   Self-deflection and all-optical beam steering in CdZnTe:V
    We observed a very large self-deflection of optical beams, along with all-optical beam steering, and electro-optic beam deflection. We observed up to 100 resolvable spots of deflection at 1W/cm2 intensity. Our results show more than 10 times more resolvable spots than in any other self-deflection result ever reported, and at a 200 time lower intensity.

  •                   Light-induced ionic polarization in CdZnTe:V
    We observed light-induced increase of the low-frequency dielectric constant in CdZnTe:V (CZT:V) semiconductor crystals, and showed that the increase is due to electric dipoles forming under illumination. Our findings suggest that CZT:V undergoes a photo-induced phase-transition at room temperature, from a non-polar to a polar phase.

  •                   Spatial modulation instability driven by light-enhanced nonlinearities in CdZnTe:V
    We demonstrated experimentally spatial modulation instability in CdZnTe:V, where the electro-optic effects are enhanced by light. We found that the total refractive index change can be expressed as sum of a uniform index change, which can exceed the value of 0.01, and a local index change which is limited to ~ 1.6 X 10-4.

  •                   Light-induced bandgap change in CdZnTe:V
    We observed a large optically-induced variation of the bandgap of the CdZnTe:V. We showed that the variation in the bandgap exceeds the value of 0.07eV, and it is fully reversible on the time scale of a few seconds. We found that, once this large value of change is obtained, the crystal shows persistent photoconductivity, and a persistent bandgap shift, that remains “frozen” many hours after the light is turned off.