No abstract

ZnS p–n homo junctions have been obtained for the first time with epitaxially grown layers having the structures of n‐ZnS:In/p‐ZnS:In, Ag, N/p‐GaAs and p‐ZnS:In, Ag, N/n‐ZnS:In/n‐GaAs. Both of these structures showed rectifying behavior which is expected for p–n junctions. The forward voltage of 3.7 V where current increases rapidly corresponds to the band gap energy of ZnS at room temperature. For reverse bias, some samples having p‐ZnS:In, Ag, N/n‐ZnS:In/n‐GaAs structure showed backward diode type character.

Molecular photonics, information processing based on strong interactions of photons and molecules, has attracted much attention, since it can fully utilize many superior properties of both photons and molecules. We have developed polymeric materials showing ultrafast absorption changes in the visible to near-infrared regions including the telecommunication wavelength by photoinduced electron transfer and reverse reactions between substituted pyridinium and its counter anion. By selecting the counter anion we succeeded in making steady and ultrafast absorption changes. Time-resolved absorption and fluorescence spectroscopy upon femtosecond laser excitation revealed reaction mechanism and ultrafast dynamics. In order to fully utilize such photoresponses in molecular photonics, we proposed guided wave mode (GWM) device composed of a prism, a low refractive index polymer film, and a photoresponsive polymer film. The reflectance in this GWM is controlled by many factors such as thickness values and complex refractive indices of two polymer layers as well as an incident angle and wavelength. We successfully achieved sensitive, all optical, and very fast control of reflectance by means of photoinduced complex refractive index changes upon femtosecond laser excitation. r

Tetrasubstituted indium or gallium phthalocyanines and their dimers bridged with various ligands were dispersed in a polymer thin film, which was spin-coated on silver thin film vacuum-evaporated on a glass slide. All-optical reflectance control was achieved by complex refractive index changes upon photoexcitation of phthalocyanines by nanosecond laser in such a guided mode geometry. They gave rise in less than ns pulse width, and a few to a few tens of microseconds decay characteristic to the lifetime of the excited triplet state. Repeated and reversible reflectance changes were achieved. Axially bridged phthalocyanine dimers showed almost the same photoresponses as monomers.