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Improved optoelectronic properties in CdSexTe1?x through controlled composition and short-range order
摘要： We employ ?rst principles methods based on density functional theory and beyond to study CdSexTe1?x alloys in the zincblende and wurtzite structures. From the cluster expansion formalism, we provide a detailed phase diagram showing a consolute temperature of 325 K, above which miscibility may be achieved. In the random solid solution, a zincblende-to-wurtzite phase boundary is found to range from Se concentrations of x = 0.5–0.6, in agreement with experiment, owing to increasing ionic character of the Cd-anion bonds. Disordered CdSexTe1?x con?gurations are modeled using special quasirandom structures, for which optoelectronic properties are computed with the hybrid HSE06 functional. Alloying is shown to cause strong bowing e?ects in the band gap and e?ective electron/hole masses, which we attribute to local structural distortions as illustrated by analysis of bond length distributions. Downward bowing in the band gap and e?ective hole mass of the zincblende structure is highlighted for its potential bene?ts in photovoltaics through increased net photocurrent. Absorption coe?cients and re?ectivity are also reported, showing promising results in zincblende CdSexTe1?x as indicated by substantial optical absorption throughout all Se concentrations. Lastly, we identify the presence of short-range order in CdSexTe1?x characterized by clustering among like atoms in order to minimize strain. The degree of clustering, which may be tuned by temperature, also controls the magnitude of the band gap. Therefore, we propose both composition and short-range order as e?ective tools to be utilized in the design and synthesis of improved solar cell absorber layer materials.
关键词： Phase diagram,Optical properties,Bandgap-bowing,Short range order,CdSexTe1?x alloys
更新于2025-09-16 10:30:52
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Bandgap bowing in crystalline (ZnO) <sub/> 1? <i>x</i> </sub> (GaN) <sub/><i>x</i> </sub> thin films; influence of composition and structural properties
摘要： Thin films of (ZnO)1?x(GaN)x with an optical bandgap between 3.3 and ～2.4 eV at room temperature for 0 ≤ x ≤ 0.2 have been grown by magnetron sputtering on (0001)-sapphire substrates. A strong dependence of the bandgap shrinkage on x for low values (x ≤ 0.07) not previously reported enables bandgap-tuned films of high crystal quality with limited distortion of the ZnO matrix suitable for optoelectronic applications. X-ray diffraction, transmission electron microscopy and Rutherford backscattering spectrometry all show a single phase and highly crystalline films. The a- and c-lattice constants are found to be 3.252 and 5.224 ? for x = 0.15, i.e. larger than that predicted by Vegard’s law. The films are highly c-axis oriented and exhibit a good heteroepitaxial relationship with the sapphire substrate, growing predominantly with aligned domains. A distinct shift in optical absorption is attributed to a shift in the bandgap, where compositions of x = 0.07 to x = 0.2 all result in bandgaps around or below 2.5 eV, while a lower GaN content increases the optical bandgap towards that of ZnO. This strong dependence of the bandgap shrinkage on x for low values (x ≤ 0.07) enables bandgap-tuned films of high crystal quality with limited distortion of the ZnO matrix.
关键词： magnetron sputtering,bandgap bowing,ZnO,GaN,alloy
更新于2025-09-04 15:30:14