MEASUREMENTS OF THE ENERGY-BAND OFFSETS OF SI1-XGEX SI AND GE1-YCY/GEHETEROJUNCTIONS/

Discontinuities in the energies of the conduction and valence bands at semiconductor heterojunctions are important parameters for device des ign. We describe experiments using X-ray photoelectron spectroscopy wi th measurements of valence-band energies with respect to core-levels o f metastable, coherently strained Si1-xGex alloy layers and of thick G e1-yCy alloy layers. For strained Si1-xGex alloys on Si, we have found that the valence band offset increased with the Ge fraction x with mo st of the offset in the valence band, We obtained a valence band offse t of 0.22 eV for x = 0.23, in good agreement with theoretical calculat ions. For Ge1-yCy alloys, we found very Little shift in the valence ba nd energies with the C fraction y, Since the optical bandgap of GeC in creased with the C fraction y, most of the offset for Ge1-yCy/Ge heter ojunction was in the conduction band, Based on the measurements of the energy band offsets of Si1-xGex/Si, we infer that the major portion o f bandgap discontinuity of Ge1-yCy on Si is in the valence band, Ge1-y Cy alloys are new metastable materials that open up a new region for g roup IV heterostructures.