Determination of valence-band offset at cubic CdSe/ZnTe type-II heterojunctions: A combined experimental and theoretical approach

Abstract

International audienceWe present a combined experimental and theoretical approach for the determination of the low-temperature valence band offset (VBO) at CdSe/ZnTe heterojunctions with underlying zincblende crystal structure. On the experimental side, the optical transition of the type II interface allows for a precise measurement of the type II band gap. We show how the excitation-power dependent shift of this photoluminescence (PL) signal can be used for any type II system for a precise determination of the VBO. On the theoretical side, we use a refined empirical tight-binding parametrization in order to accurately reproduce the band structure and density of states around the band gap region of cubic CdSe and ZnTe and then calculate the branch point energy (also known as charge neutrality level) for both materials. Because of the cubic crystal structure and the small lattice mismatch across the interface, the VBO for the material system under consideration can then be obtained from a charge neutrality condition, in good agreement with the PL measurements

Optical determination of the band gap and band tail of epitaxial Ag2ZnSnSe4 at low temperature

“…In the present case, the time-dependent spectra are plotted, on a semi-logarithmic scale, for time delays in a geometric series 30 . In such a scheme, if the PL decay were following a power law dependence on time 31,32 , the intensity maxima between two successive curves should be visually equidistant on this semi-logarithmic plot: it is not the case here, at least for times up to ≈ 25 ns, as the larger the time, the closer the spectra look, which evidences that the PL intensity peak decrease is slower than any power law, therefore slower than any exponential. For times larger than ≈ 25 ns, the data is not so clear, and a power law behaviour cannot be fully excluded.…”

Tight-binding branch-point energies and band offsets for cubic InN, GaN, AlN, and AlGaN alloys

“…The importance of the choice of the band structure method in BP calculations has already been discussed in Ref. 26. It has been pointed out that a suitably parametrized empirical tight-binding model will allow for a flexible fit to a large parameter space; the input parameters can then be either chosen from experiments or from results of more sophisticated calculation schemes.…”

“…Note that a modification of the model such as in Ref. 26 is not necessary here, as the spin-orbit interaction is comparatively weak in the III-nitrides, which leads to spin splittings two orders of magnitude smaller than the band gap.…”

“…1 suggests, this band subset can be justified by the much larger dispersion of the lowest VB. It should however be kept in mind that this set is obviously not suitable for several II-VI materials, 26 and the choice of bands certainly remains a major source of uncertainties in the BP calculation. For that reason, we carefully recommend the same uncertainty range of 0.2 eV as given by Schleife et al…”

Interfacial chemistry in a ZnTe/CdSe superlattice studied by atom probe tomography and transmission electron microscopy strain measurements

“…The interesting optical and structural properties of ZnTe/CdSe superlattices (SLs) make them promising candidates for photovoltaic devices. The type‐II band alignment between ZnTe and CdSe allows the direct spatial separation of the photo‐generated carriers (Mourad & Richters, ). By varying the SLs layer thicknesses and the number of periods, it is possible to adjust the absorption of the solar cell to match the visible spectrum (Boyer‐Richard et al ., ).…”