Observation of strain relaxation in Si1-xGex layers by optical and electrical characterisation of a Schottky junction

We have studied the effect of the strain relaxation on the band-edge alignments in a Pt/p-Si_1-xGe_x Schottky junction with x=0.14 by internal photoemission spectroscopy and current–voltage measurements. We have shown that the variations in the band-edge alignments can be observed directly by measuring the optical and electrical properties of a simple Schottky junction. The strain in the Si_1-xGe_x layer has been partially relaxed by thermal treatments at two different temperatures. The degree of relaxation and other structural changes have been determined by a high-resolution X-ray diffractometer. Both optical and electrical techniques have shown that the barrier height of the Pt/Si_0.86Ge_0.14 junction increases with the amount of relaxation in the Si_1-xGe_x layer. This shows that the valence-band edge of the Si_1-xGe_x layer moves away from the Fermi level of the Pt/Si_1-xGe_x junction. The band-edge movement results from the increase in the band gap of the Si_1-xGe_x layer after the strain relaxation. This result agrees with the theoretical predictions for the strain-induced effects on the Si_1-xGe_x band structure. Received: 18 October 2000 / Accepted: 19 December 2000 / Published online: 23 March 2001