Microscopic study of semiconductor heterojunctions: Photoemission measurement of the valance-band discontinuity and of the potential barriers

We report on synchrotron-radiation photoemission measurements of the valence-band discontinuity and of the Fermi-level position for 25 different interfaces involving group-IV, III-V, and II-VI semiconductor substrates and Ge or Si overlayers. A comparison is made between our measured discontinuities and the predictions of current theoretical models. We find the best agreement with empirically corrected versions of the models of Harrison and of Frensley and Kroemer. However, we present a new empirical rule based on our present results and on those of other authors which yields even more accurate predictions of band discontinuities. The measured Fermi-level-pinning position of each substrate is the same for both Ge and Si overlayers. This result is discussed in terms of the "defect model" of Fermi-level pinning, originally developed for Schottky barriers.