Qiuhua Nie

New far-infrared transmitting Te-based chalcogenide glasses

This study reports on the synthesis of tellurium-based glasses that have a wide transmission far beyond the second atmospheric window. Several far-infrared(IR) transmitting glass systems including Ge-In-Te, Ge-Ga-Te, as well as some compositions containing alkali halides (KI, CsI) or metal halides (PbI2, CuI, AgI, CdI2 or ZnI2) are reported. Their glass-forming ability, thermal stability, and IR transmitting property are investigated. The results show that the broad absorption peak in the 15–20 μm disappear in the Fourier-transform infrared (spectrometer) spectra when gallium is replaced by indium. Te-based chalcogenide glasses containing metal-halides show superior glass-forming ability and better thermal stability than those containing alkali halides. Among these glasses, the ΔT of glass composition 65GeTe4-17In2Te6-18AgI can be as great as 115 °C. In ternary system, the glass composition Ge16Te69(AgI)15 (ΔT = 120 °C) is stable enough toward crystallization in combination with broad transmission region ...

Improved thermal and electrical properties of Al-doped Ge2Sb2Te5 films for phase-change random access memory

Alx(Ge2Sb2Te5)100−x materials with different Al contents are systemically studied for applications in phase-change random access memory (PRAM) devices. Al-doped Ge2Sb2Te5 (GST) films show better thermal stability than GST because they do not have phase transformation from face-centred cubic (fcc) to hexagonal at high annealing temperatures. As the Al content increases, the resistance in both amorphous and crystalline phases improves and there is four to five orders of magnitude difference in the resistance between the amorphous and crystalline phases, all of which are helpful in achieving a higher On/OFF ratio for PRAM. In addition, the introduction of Al into the GST films can increase the optical band gap that is favourable to decrease the threshold current of PRAM devices. Raman spectra show that a significant change in the local bonding arrangement around Sb atoms has occurred due to the phase transformation from fcc to hexagonal in the GST film but this can be suppressed by Al addition during the crystallization process. All these results confirm that Al-doped GST films are suitable for use in PRAM.

Characterization of Physical Properties for Zn-Doped Sb3Te Films

Compared with an undoped Sb3Te film, a Zn26.28(Sb3Te)73.72 film exhibits high crystallization temperature (~202 °C) and activation energy of crystallization (~3.28 eV), resulting in stability at high temperatures with an extrapolated life-time of 10 years at 130 °C. The crystalline resistance increases and the amorphous/crystalline resistance ratio is about 104, which is helpful to achieve a high On/OFF ratio. The optical band gap of a Zn26.28(Sb3Te)73.72 film decreases as it transforms from the amorphous phase to the crystalline phase. The average kinetic exponent (n) of the film is 2.44, indicating that its crystallization mechanism is of the nucleation-dominated type.

Phase change and optical band gap behavior of Ge-Zn-Te chalcogenide films

Glassy alloys with composition of Ge20ZnxTe80-x (x=0, 5, 10, 15at%) were prepared by conventional melt-quenching method, which were subsequently used as target for thermal evaporation (TE) technique under vacuum. The Ge-Te-Zn chalcogenide thin films were characterized with XRD and Transmittance spectra. XRD measurements indicate that there is an amorphous-to-crystalline phase transition. The GeTe crystallines were suppressed in the film with x=5 after annealing while the GeTe crystallines become predominant and the formation of Te crystallines were suppressed with Zn content increasing. Optical band gap is estimated using Taucs extrapolation and is found to decrease from 0.509 to 0.395eV in as-deposited films with x=0, 5, 10., while the optical band gap increases to 0.555eV in as-deposited films with x=15. The similar behavior is also observed in the annealed films. A comparison of optical band gap of various films illustrates the thermally-induced effects.