Determination of the bowing parameter of the split-off band inCd0.8Zn0.2Te(100) by angle-resolved photoemission spectroscopy

Angle-resolved photoemission spectroscopy is used to measure the width ${\mathrm{\Omega }}_{\mathrm{s}.\mathrm{o}.\mathrm{}}$=${\mathrm{\Gamma }}_7$-${\mathit{X}}_6$ of the split-off valence band in ${\mathrm{Cd}}_{0.8}$ ${\mathrm{Zn}}_{0.2}$Te(100). We find an increase in the alloy bandwidth which is ∼2 times larger than the value expected from a linear alloy model (Vegard’s rule). Using CdTe as a reference material, we determined a bowing parameter ${\mathit{b}}_{\mathit{p}}$∼0.65 eV for the split-off-band width in ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Zn}}_{\mathit{x}}$Te alloys. The virtual-crystal approximation (VCA) works well for the upper valence bands but fails to describe the more localized d states. Chemical differences and the size mismatch between Cd and Zn atoms lead to pronounced deviations from the VCA behavior. The appearance of distinctly split Cd 4d- and Zn 3d-band emissions which we observe is outside the scope of the VCA, lending support to more sophisticated structural models which incorporate disparate Cd and Zn atoms for binary semiconducting alloys.