Valence-band structure and final states in photoemission from (112¯0) surfaces of CdS and CdSe

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Abstract
The application of angle-resolved photoelectron spectroscopy with synchrotron radiation as the source for excitation is demonstrated to be a powerful technique for determining valence-band dispersions as well as for yielding information on which final states are involved in the process. By recording electron-energy-distribution curves in normal emission from the (112¯0) surfaces of wurtzite single crystals of CdS and CdSe, transitions between valence-band states and conduction-band states along the Γ–M line have been studied. Parity rules have been observed by exciting the transitions with radiation polarized parallel or perpendicular to the mirror plane of the crystal. Eleven critical-point energies have been determined and are compared with theoretical predictions and with the results of previous experiments. By assuming direct transitions it is possible to determine the valence-band dispersions along Γ–M and, through fitting procedures, to derive the relevant final states. The results indicate that the valence-band structure is well described by the latest calculations, except for an underestimation of the width of the upper valence bands. The final states are found to deviate very little from simple parabolic bands in the normal direction, throughout the energy region studied.