Ohmic contacts for group III-V n-type semiconductors using epitaxial germanium films

Claim 1

A method for making an ohmic contact to an n-type III-V semiconductor material, comprising the steps of: cleaning the material successively in trichloroethylne, acetone, and deionized water; etching said material in diluted hydrofluoric acid; rinsing the material in deionized water; re-etching said material in a hydrofluoric acid-hydrogen peroxide solution; re-rinsing the material in deionized water; placing the material in an oil-free vacuum of at least 2×10 -7 Torr and maintaining the material at a temperature of 575° C. ± 2° C. for approximately fifteen minutes for desorbing any surface oxides of the material; forming an epitaxial layer of germanium on said material in said vacuum, the material being maintained at a temperature sufficient to develop an epitaxial growth for completely covering and uniformly wetting said material; forming an overlayer of a metal selected from the group consisting of nickel and a refractory metal from Groups V and VI of the Periodic Table on said epitaxial layer for developing a semiconductor structure, said material being maintained at a temperature sufficient to minimize sticking coefficients of residual gases without causing a reaction between the overlayer and the material during the forming of the overlayer; and annealing said structure at a temperature sufficient for diffussing the overlayer and epitaxial layer with said material and for forming said ohmic contact, said temperature being within the range of 350° C. and 525° C. for nickel and within the range of 400° C. to 500° C. for a refractory metal from Groups V and VI of the Periodic Table.

Claim 2

A method for making an ohmic contact to an n-type III-V semiconductor material, comprising the steps of: cleaning the material successively in trichloroethylne, acetone, and deionized water; etching said material in diluted hydrofluoric acid; rinsing the material in deionized water; re-etching said material in a hydrofluoric acid-hydrogen peroxide solution; re-rinsing the material in deionized water; placing the material in an oil-free vacuum of at least 2×10 -7 Torr and maintaining the material at a temperature of 575° C. ± 2° C. for approximately fifteen minutes for desorbing any surface oxides of the material; forming an epitaxial layer of germanium on said material in said vacuum, the material being maintained at a temperature sufficient to develop an epitaxial growth for completely covering and uniformly wetting said material; forming an overlayer of a metal selected from the group consisting of nickel and a refractory metal from Groups V and VI of the Periodic Table on said epitaxial layer for developing a semiconductor structure, said material being maintained at a temperature sufficient to minimize sticking coefficients of residual gases without causing a reaction between the overlayer and the material during the forming of the overlayer; and annealing said structure at a temperature sufficient for diffussing the overlayer and epitaxial layer with said material and for forming said ohmic contact, said temperature being within the range of 350° C. and 525° C. for nickel and within the range of 400° C. to 500° C. for a refractory metal from Groups V and VI of the Periodic Table.