Photoemission studies of core level shifts in HgCdTe, CdMnTe, and HgZnTe

Abstract

We report here the photoemission studies of core level shifts in Hg1−xCdxTe, Cd1−xMnxTe, and Hg1−xZnxTe alloys. The cation core level binding energies relative to the valence-band maximum (VBM) are measured as a function of composition. In Hg0.7Cd0.3Te, the Hg 5d level shifts to lower binding energy by 0.1 eV whereas the Cd 4d levels shift to higher binding energy by 0.25 eV upon alloying (relative to their binaries). In Cd1−xMnxTe and Hg1−xZnxTe, such behavior is not observed: the binding energies of the Cd 4d level in CdTe and Cd0.55Mn0.45Te are the same; the binding energies of the Hg 4d level in HgTe and Hg0.84Zn0.16Te are the same also. By using the Born–Haber cycle, we have calculated core level binding energies relative to the VBM in the context of tight-binding theory. Compared to our measurements the calculated core level shifts upon alloying in HgCdTe are too small to account for the observed values. We attribute the discrepancy to the existence of natural valence-band offset between HgTe and CdTe, which has been considered to be zero in our calculation. The natural valence-band offset between HgTe and CdTe deduced from our experiment is 0.35 eV. Following the same line of argument, the natural valence-band offsets between CdTe and the hypothetical zinc-blende MnTe, and between HgTe and ZnTe, are small.