The orientation independence of the CdTe-HgTe valence band offset as determined by x-ray photoelectron spectroscopy
Summary (1 min read)
- Self-consistent tight-binding (SCTB) calculations by Munoz et al  have predicted a large dependence on orientation, 180 meV between the (100) and (HO) surfaces (AEv = 0.46 and 0.28 eV, respectively).
- In contrast, Van de Walle et al  , using self-consistent local density functional methods, predict no surface dependence, i.e. AEv = 0.27 and 0.28 eV, respectively.
- In fact a more general study by the latter authors suggests that this independence is a characteristic of a number of important interfaces, e.g. CdTe•-HgTe, AIAs-GaAs and Si-Ge.
- Indeed this has been shown to be the case for the GaAs-AIAs heterojunction  .
- In order to determine which is correct for the CdTe-HgTe heterojunction the authors have investigated the effect of surface orientation as well as the effect of interface structure on the valence band offset.
2. Experimental details
- The resulting heterojunctions were transferred via an ultra-high-vacuum transfer system and investigated by XPS under nearly in situ conditions.
3. Results and discussion
- First the HgTe and CdTe spectra were co~bined and fitted to the heterojunction spectrum by means of a least-square procedure.
- In order to more accurately determine the position of the peak.
- The results for the (100), ( 110) and (llJ)B orientations are tabulated in table 1. in the first case HgTe was grown on (100)-(2 x 1) and (111)B-(1 x 1) Te-stabilized CdTe surfaces respectively, whereas in the second case HgTe was grown on a mixed surface with half-order reconstruction in both the [OH] and  azimuths for the (lOO) orientation and (2v13 x 2j3)R30° reconstruction for (111)B.
- In each case the two corresponding values are the same within the experimental uncertainities given in table 1 .
- Furthermore, 6.Ev has been determined to be 0.37 ± 0.07 eV, in good agreement with the literature    .
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