VUV Ellipsometry on Beryllium Chalcogenides

We have determined the dielectric function (DF) of beryllium chalcogenides between 2.5 and 25 eV using an ellipsometer operating with synchrotron radiation in the VUV range. The VUV ellipsometer is, in particular, useful for the characterization of wide band gap semiconductors since the spectral range of spectrometers equipped with conventional light sources is limited to below 6 eV. Beryllium chalcogenides are a relatively new class of material with still unknown optical and electronic properties. Here we determine the dielectric function of BeTe and BexZn1—xSe for the full composition range (0 ≤ x ≤ 1). We verify that they are wide band gap semiconductors with their direct band gaps at 4.2 eV (BeTe) and 5.55 eV (BeSe).