Nonalloyed ohmic contacts to n-Si using a strained Si0.50Ge0.50 buffer layer

Abstract
We have grown an 80‐Å‐thick strained Si0.50Ge0.50 layer on n‐Si by molecular‐beam epitaxy. The strained layer is used to lower the Schottky barrier height for making a nonalloyed shallow ohmic contact to the n‐Si. X‐ray photoelectron spectroscopy was employed to investigate the Si 2p and Ge 3d core‐level binding energies of the strained and the relaxed Si0.50Ge0.50 and to determine their relative Fermi‐level positions. Rutherford backscattering and Auger depth profiling were employed to determine the contact reactions using Ti, W, or Pt as contact metals. In the case of Pt, a 500‐Å W diffusion barrier can protect the ohmic behavior up to 550 °C for 30 min. The specific contact resistance of the metal/Si0.50Ge0.50/n‐Si contact extracted from the D‐type cross‐bridge Kelvin resistor was 3.5×10−5 Ω cm2.