X-ray photoemission and bremsstrahlung isochromat spectroscopy of bulk single crystalline SixGe1−x alloys

Abstract The electronic structures of the valence and the conduction bands of bulk single crystallineSi x Ge − x alloys ( x = 0, 0.05, 0.135, 0.18, 0.47, 1) are studied by X-ray photoemission spectroscopy and bremsstrahlung isochromat spectroscopy. The valence band maxima monotonically shift to a lower binding energy side as the composition x increases. The conduction band minima rapidly shift to the high binding energy side in the small composition range x = 0−0.18, and then slowly shift on the composition in the region above x = 0.18. As a result, the energy gaps increase as a quasi-linear function of composition x with a slope discontinuity at x = 0.18. We can quantitatively see from the results that the discontinuity of the band gap obtained by the optical absorption measurement mainly originates from the shifts of the conduction band minima.