| Summary: | 碩士 === 國立東華大學 === 材料科學與工程學系 === 96 === In the study, structural, optical and electrical properties of crystalline As2( Te1-xSx )3 ( x=0、0.1、0.3 ) and As2( Se1-xTex )3 ( x=1.0、0.6、0.4 ) were characterized. The crystals were grown by vertical Bridgman method.
The lattice parameters were determined by X-ray diffraction . The interband transitions were characterized by thermoreflectance ( TR ) spectroscopy in the energy range of 0.7-6.0 eV, at 50K and 300K. The measurements of resistivity, mobility and carrier concentration werecarried out by resistivity Hall measurement in the temperature range of 20K to 300K.
The crystalline of As2Te3 is a direct semiconductor with are observed band gap of about 0.95 eV at room temperature ( 300K ). There are three interband transitions ( A、B and C ) in the TR spectra of the crystals. A is the band gap transition ( 0.95-2.594 eV ) . C comes from the As-As bonding ( 3.229-3.134 eV ). When more sulfur incorporated in As2( Te1-xSx )3 shifts to higher energy. The band gap ( A ) shifts to higher energy. All the three interband transitions (A、B and C) of the crystals shift to higher energy when the temperatures decrease from 300K to 50K.
Observing from the resistivity and Hall measurements, the crystalline of As2Te3 is a semiconductor . When more sulfur incorporated in As2( Te1-xSx )3 ( x=0.1、0.3 ), the resistivity remains nearly unchange.
For As2Se3, the crystalline of As2Se3 is a direct semiconductor with band gap of 1.63 eV at room temperature ( 300K ). There also three interb -and transition ( A、B and C ) observed in the TR spectra. A is the band gap ( 1.63-0.95 eV ). C is coming from the As-As bonding ( 3.229-3.116 eV ) the same as that of crystalline As2( Te1-xSx )3 ( x=0.1、0.3 ). When more tellurium incorporated in As2( Se1-xTex )3 ( x=0.6、0.4 ) and As2( Se1-xTex )3 ( x=0.6、0.4 ) the band gap of these materials ( A ) moves to lower energy.
The resistivity of crystalline As2Se3 is over 1010 ( Ω-cm ) . When tellurium incorporated in As2( Se1-xTex )3 ( x=0.6、0.4 ), the resistivity dramatically goes from very high ( ~1010 Ω-cm for As2Se3 ) down to a low value [ ~10 Ω-cm for As2( Se1-xTex )3 ].
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