A novel route to fibers with volatile crystalline semiconductor cores part 2: Selenides and phosphides

Abstract

The flux assisted molten core method, previously employed to fabricate glass-clad crystalline GaAs core fiber, is applied here to realize crystalline selenide and phosphide cores. These semiconductor families show great promise in photonics, optoelectronics, and thermoelectrics, although their volatility has previously prohibited successful fabrication utilizing the conventional molten core method. Through the introduction of a flux, the alloy melt temperature and associated vapor pressure can be sufficiently reduced to permit thermal drawing of the melt inside a glass cladding into fiber. Reported here are demonstrations of crystalline selenide and phosphide cores. Also reported is the CO2 laser post processing of a ZnSe core fluxed with Cu8GeSe6, which resulted in lateral segregation of the ZnSe phase from the flux. X-ray diffraction and electron microscopy were deployed to determine the resulting ZnSe, InP and flux alloy phases and elemental distributions in the fiber core. X-ray diffraction of the InP: flux and most of the ZnSe: flux systems showed intermetallic flux phases that were not present on the phase diagrams reported in the literature. Formation enthalpy and phase diagrams of the intermetallic phases at room temperature were used to determine which observed phases were thermodynamically stable or meta-stable. The results indicate that the influences at play are primarily thermodynamic, but in some cases, kinetics plays a role during the fabrication of these fibers, forming metastable phases. Lastly, a review and discussion of the new demands on cladding glasses is presented for laser post-processing such fibers. This work demonstrates an approach to incorporating volatile and incongruently melting phases, that are not compatible with the standard molten core method, to realize novel in-fiber optoelectronic compositions.