Using first‐principles band‐structure theory we have systematically calculated the (i) alloy bowing coefficients, (ii) alloy mixing enthalpies, and (iii) interfacial valence‐ and conduction‐band offsets for three mixed‐anion (CuInX2, X=S, Se, Te) and three mixed‐cation (CuMSe2, M=Al, Ga, In) chalcopyrite systems. The random chalcopyrite alloys are represented by special quasirandom structures (SQS). The calculated bowing coefficients are in good agreement with the most recent experimental data for stoichiometric alloys. Results for the mixing enthalpies and the band offsets are provided as predictions to be tested experimentally. Comparing our calculated bowing and band offsets for the mixed‐anion chalcopyrite alloys with those of the corresponding Zn chalcogenide alloys (ZnX, X=S, Se, Te), we find that the larger p−d coupling in chalcopyrite alloys reduces their band offsets and optical bowing. Bowing parameters for ordered, Zn‐based II‐VI alloys in the CuAu, CuPt, and chalcopyrite structures are present...

Band offsets and optical bowings of chalcopyrites and Zn‐based II‐VI alloys

The relativistic band structure and band-gap bowing factors of ternary II-VI semiconductor alloys containing Cd, Zn, Se and Te are calculated by the ab initio self-consistent pseudopotential method with spin-orbit correction. The disorder in these alloys is modelled by the virtual crystal approximation (VCA). The numerical results thus obtained are compared with experimental data from photoluminescence spectroscopy. The experimental band-gap bowings for this family of alloys are always concave upwards. However, CdSexTe1-x and ZnSexTe1-x in general show much larger bowing factors than Cd1-xZnxSe and Cd1-xZnxTe. The former two alloys show a minimum in the band gap versus composition curve near x=0.35 while the latter two have it at x=0. Most of these qualitative trends are well explained by VCA. However, in order to explain the large bowing in the first two alloys, some kind of local order has to be incorporated in the calculation. It was found that a local cluster with AuCu-I-like structure, when relaxed, has quite a significant contribution to the bowing factors. The splittings in the band structure due to both spin-orbit and structural relaxation effects are also discussed.

https://iopscience.iop.org/article/10.1088/0953-8984/7/14/017/pdf

Relativistic band structure of ternary II-VI semiconductor alloys containing Cd, Zn, Se and Te

We use a combination of optical and soft x-ray fluorescence techniques to investigate the composition dependence of the band edge energies in ZnSe(1-x)Te(x) and ZnS(1-x)Te(x) alloys. The results reveal entirely different origins of the large bandgap bowing for alloys with small and large Te content. On the Te-rich side, the reduction of the bandgap is well explained by the band anticrossing interaction between the Se or S localized states and the ZnTe conduction band states. On the Se or S-rich side, an interaction between the localized Te states and the degenerate GAMMA valence bands of ZnSe or ZnS is responsible for the bandgap reduction and the rapid increase of the spin-orbit splitting with increasing Te concentration. Results of soft x-ray fluorescence experiments provide direct evidence for the valence band anticrossing interaction. The bandgap bowing over the entire composition range is accounted for by a linear interpolation between the conduction band anticrossing and valence band anticrossing models.

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Origin of the large band-gap bowing in highly mismatched semiconductor alloys

We investigate the doping behavior of ZnSe/ZnTe short period superlattices. p‐type doping is achieved with a dc nitrogen plasma source, n‐type doping with chlorine from a ZnCl2 Knudsen source. Even a small Te content has a strong positive effect on p doping: Doping levels in the upper 1019 cm−3 range are achieved, and ohmic contacts can be obtained even for low carrier concentrations. The data are in excellent agreement with a theory based on the amphoteric native defect model. The opposite is valid for n doping: At Te concentrations above 20% electron concentrations are below 1016 cm−3. As a possible way to get both good n‐ and p‐type doping at the same lattice constant we propose the use of the quaternary compound Zn(1−y)Mg(y)Se(1−x)Te(x).

/pdf/doping-of-zinc-selenide-telluride-z0x0woi5q1.pdf

Doping of zinc-selenide-telluride

Excitons in vertically stacked type-II quantum dots experience the topological magnetic phase and demonstrate the Aharonov-Bohm oscillations in the emission intensity. Photoluminescence of vertically stacked ZnTe/ZnSe quantum dots is measured in magnetic fields up to 31 T. The Aharonov-Bohm oscillations are found in the magnetic-field dependence of emission intensity. The positions of the peaks of the emission intensity are in a good agreement with numerical simulations of excitons in stacked quantum dots.

/pdf/optical-aharonov-bohm-effect-in-stacked-type-ii-quantum-dots-owo67bdt6s.pdf

Optical Aharonov-Bohm effect in stacked type-II quantum dots

We report a systematic study of the optoelectronic properties of ZnSe1−xTex alloys grown by molecular beam epitaxy over the entire range of compositions. The band‐gap energy as a function of the composition presents a minimum at x≂0.65. The main luminescence emission observed at 5 K becomes narrower and closer to the band‐gap energy as we increase the Te content. The linewidth and the difference between the emission peak and band‐gap energy decrease significantly with increasing x and present a break in the slope at x≂0.65.

Evolution of the band gap and the dominant radiative recombination center versus the composition for ZnSe1−xTex alloys grown by molecular beam epitaxy

Optical measurements have been used to study the biaxial tensile strain in heteroepitaxial ZnTe gronw by molecular-beam epitaxy on both GaAs and GaSb substrates, and its effect on the low-temperature photoluminescence (PL) spectrum of the material. The observed strain (0.92×10 -3 for ZnTe/GaAs and 0.45×10 -3 for ZnTe/GaSb) agrees with that expected for differential thermal contraction from the growth temperature to low temperature, based on the difference in thermal expansion coefficients

Effects of thermal strain on the optical properties of heteroepitaxial ZnTe.

Molecular beam epitaxy of Zn(Se,Te) alloys and superlattices

ZnSe1−xTex ternary alloy has been grown over the entire range of composition by molecular beam epitaxy on GaAs and InP substrates A precise control of the composition is achieved by growing this material under Zn‐rich conditions For low Te concentrations, However, significant Te surface segregation is observed, which may be due to surface energy minimization The band‐gap energy has been measured over the entire range of composition and presents a very strong bowing with a minimum energy of 205 eV for a Te concentration of 065

Molecular beam epitaxy of ZnSe1−xTex ternary alloys

Efficient p doping of ZnTe by arsenic has been achieved using a Zn3As2 effusion cell Doping levels of ZnTe/GaAs can be controlled from 1016 to 1018 cm−3 The carrier concentration is independent of the substrate used, ZnTe:As/GaAs and ZnTe:As/InP giving similar results Spectral photoconductivity and low‐temperature photoluminescence, however, show an increase of deep levels for doping levels higher than 1017 cm−3 but electrical measurements show no saturation for doping as high as 1018 cm−3

F. S. Turco-Sandroff

Papers

Evolution of the band gap and the dominant radiative recombination center versus the composition for ZnSe1−xTex alloys grown by molecular beam epitaxy

Effects of thermal strain on the optical properties of heteroepitaxial ZnTe.

Molecular beam epitaxy of Zn(Se,Te) alloys and superlattices

Molecular beam epitaxy of ZnSe1−xTex ternary alloys

Arsenic‐doped P‐type ZnTe grown by molecular beam epitaxy