Almost all metal-semiconductor or Schottky contacts exhibit rectifying behaviour which is caused by a depletion layer on the semiconductor side of the interface. The electronic properties of a Schottky diode are characterised by its barrier height which is the energy difference between the top of the valence band of the semiconductor and the Fermi level at the interface. The physical mechanism primarily determining barrier height is provided by the decay of the metal's electron wavefunctions into the semiconductor in the energy range between the top of the valence band and the Fermi level where the metal conduction band overlaps the semiconductor band gap. These wavefunction tails are described as the continuum of metal-induced gap states (MIGS) which are derived from the virtual gap states of the complex semiconductor band structure.

https://iopscience.iop.org/article/10.1088/0034-4885/53/3/001/pdf

On the physics of metal-semiconductor interfaces

Abnormal rectifying behavior has been observed in molybdenum/silicon Schottky barrier diodes produced by ion‐beam sputter deposition of Mo on single‐crystal Si. Rectifying, rather than ohmic contacts are obtained on p‐type Si, while ohmic behavior is seen on n‐type Si. These results are contrary to the usual results reported in the literature, and are shown to be caused by ion‐beam surface damage of Si. The damage does not simply cause a surface layer of high‐recombination velocity, but rather tends to bend the Si band edges downwards, irrespective of the Si conductivity type.

Effect of ion‐beam sputter damage on Schottky barrier formation in silicon

Hydrodynamic particle removal from surfaces

Study of Indium Tin Oxide (ITO) for Novel Optoelectronic Devices

Reactive ion etching of silicon with NF3 gas has been found to alter the silicon surface such that the Schottky barrier height is systematically changed with ion energy. The energetic ions introduce a net positive surface charge which increases the barrier height on  p‐Si and decreases it on n‐Si. The Schottky barrier modification is found to be a function of ion energy as well as gas plasma used.

Modification of Schottky barriers in silicon by reactive ion etching with NF3

The properties of d.c. sputtered molybdenum-silicon Schottky diodes are described. Although it is possible to produce near ideal characteristics when a low sputtering voltage is used for a short time, increased voltage and time lead to significant deviation from the ideal. A model is proposed which is capable of explaining most features of the observed C-V and I-V characteristics. This model assumes that sputtering damage causes donor-like traps to be created close to the semiconductor surface. It is found that an exponential distribution of traps with characteristic length in the range 10–100 A and an energy level of 0·43 eV below the conduction band is sufficient to account for the observed characteristics. The modification to the I–V characteristics is due to tunnelling through the top of the Schottky barrier where it is narrowed by the presence of the excess trapped charge.

Francis H. Mullins

Papers

The effects of sputtering damage on the characteristics of molybdenum-silicon Schottky barrier diodes