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The energy gap Eg of Zn1-xMgxSySe1-y epitaxial layers as a function of composition and temperature

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Abstract

The energy gap of zinc-blende epitaxial layers grown by molecular beam epitaxy has been determined over a wide range of composition using optical transmission and reflection and an empirical formula for the energy gap at room temperature is also given. In addition in situ spectroscopic ellipsometry was used in order to determine the temperature dependence of the energy gap between room temperature and the growth temperature of alloys with compositions x, y as used in cladding layers and waveguides for blue - green light-emitting devices.

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... eV with the increase in sulfur composition and is summarized in table 1. The dependence of the energy gap of a ternary A II B VI C VI alloy on the composition x at a fixed temperature can be described by the empirical equation [32]: The variation in band gap with composition is found to be nonlinear, showing a similar bowing; the degree of nonlinearity can be fitted to the following quadratic equation: ...
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Keywords: thin films of ZnS x Se 1−x compounds, thermal evaporation of ZnS and ZnSe powders mixture, EXAFS spectroscopy, x-ray diffraction, Raman spectroscopy, band gap Abstract Interest to ZnS x Se 1−x alloys is due to their band-gap tunability varying S and Se content. Films of ZnS x Se 1−x were grown evaporating ZnS and ZnSe powder mixtures onto SiO 2 , NaCl, Si and ITO sub-strates using an original low-cost method. X-ray diffraction patterns and Raman spectroscopy, show that the lattice structure of these films is cubic ZnSe-like, as S atoms replace Se and film compositions have their initial S/Se ratio. Optical absorption spectra show that band gap values increase from 2.25 to 3 eV as x increases, in agreement with the literature. Because S atomic radii are smaller than Se, EXAFS spectra confirm that bond distances and Se coordination numbers decrease as the Se content decrea-ses. The strong deviation from linearity of ZnSe coordination numbers in the ZnS x Se 1−x indicate that within this ordered crystal structure strong site occupation preferences occur in the distribution of Se and S ions. The behavior is quantitatively confirmed by the strong deviation from the random Ber-noulli distribution of the three sight occupation preference coefficients of the strained tetrahedron model. Actually, the ternary ZnS x Se 1−x system is a bi-binary (ZnS+ZnSe) alloy with evanescent forma-tion of ternary configurations throughout the x-range.
... [37]. b Ref. [38]. c Ref. [39]. ...
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Atomic layer epitaxy (ALE) is investigated for the binary semiconductor MgTe. Reflection high‐energy electron‐diffraction studies on MgTe atomic deposition, together with x‐ray diffraction, high‐resolution transmission electron microscopy, and photoluminescence experiments on ALE‐grown CdTe/MgTe superlattices are reported. They reveal that an autoregulated growth at 0.7±0.1 MgTe monolayer/ALE cycle can be achieved in a substrate temperature range between 260 and 300°C. New values of the zinc‐blende MgTe lattice parameter, a MgTe =6.420 ±0.005 Å, of the ratio of the elastic coefficients 2<sup>c 12 </sup> c11 (MgTe)=1.06, and of the 300 K MgTe band gap, E G =3.5 eV, are obtained by correlating x‐ray‐diffraction and optical results. © 1996 American Institute of Physics.
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We have experimentally investigated refractive indices n of Zn x Mg 1-x S y Se 1-y , using the ellipsometry method and reflection‐spectrum measurement. The samples are epitaxial films of undoped Zn x Mg 1-x S y Se 1-y grown by molecular beam epitaxy on semi‐insulating GaAs substrates. The obtained dispersion relations of n in the transparent region are classified by the band‐gap energy E g . We have found that the refractive index n of Zn x Mg 1-x S y Se 1-y decreases as E g increases. These results will be available for the design of blue laser diodes containing ZnMgSSe.  
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A relation for the variation of the energy gap (Eg) with temperature (T) in semiconductors is proposed. Eg ≐ E0 - αT2/(T+β) where α and β are constants. The equation satisfactorily represents the experimental data for diamond, Si, Ge, 6H-SiC, GaAs, InP and InAs.
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We propose a new material, ZnMgSSe, as the possible cladding layer of blue laser diodes. The band-gap energy can be varied from 2.8 to near 4 eV, maintaining lattice-matching to a (100) GaAs substrate. From the quarternary data, the band-gap energies of MgS and MgSe (zincblende structure) are estimated to be about 4.5 and 3.6 eV, and the lattice constants are 5.62 and 5.89 Å, respectively. The refractive index of ZnMgSSe lattice-matched to GaAs is smaller than that of ZnSSe lattice-matched to GaAs. ZnMgSSe therefore meets the requirements of the cladding layer of ZnSSe for fabricating blue laser diodes.