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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
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Mg induced compositional change in InGaN alloys
摘要： Tunnel junctions are indispensable elements of multi-junction solar cells. The fabrication of InGaN tunnel junctions requires the growth of degenerately doped n- and p-type layers. While highly doped n-type InGaN films have been demonstrated, the growth of degenerately p-doped InGaN films and the fabrication of high indium fraction InGaN tunnel junctions is still to be demonstrated. We present an investigation of the effect of Mg doping on the InGaN crystal properties over a large range of Mg fluxes and InN mole fractions in the range from 30% to 40%, using multiple characterization techniques. InGaN thin films were grown on GaN/sapphire templates and doped with Mg using plasma assisted molecular beam epitaxy (PAMBE). We have found that the Mg concentration in the film increases linearly with the Mg beam equivalent pressure (BEP) at first, followed by a saturation at ~4x1021 cm-3 similar to the Mg doping behavior reported for GaN. The growth rate of the alloy changes by more than 50% with the changes in the surface availability of Mg. These effects can be explained through the saturation of the atomic sites available for incorporation in the case of Mg concentration saturation and by the passivation of the free nitrogen radicals in the case of the growth rate variation. The incorporation of In and Ga depends on the flux ratio (ΦIn + ΦGa) /(ΦMg) at the growth surface and it is shown that the decrease of this ratio below a threshold of ~2000 causes the almost complete loss of In and the formation of a new quaternary wide band gap semiconductor alloy (InGaMg)N.
关键词： In incorporation,(InGaMg)N alloy,Plasma-assisted molecular beam epitaxy,Tunnel junction,Mg-doped P-type InGaN,InGaN
更新于2025-09-04 15:30:14