Contact for semiconductor device

1. A method of preparing an n-contact in a GaN semiconductor, said method comprising:

disposing a layer of a first metal on a GaN semiconductor to define a semiconductor interface, said GaN semiconductor being n-doped and having a semiconductor work function, said first metal being in sufficient amount to impart a first property in said layer; and

after disposing said layer, diffusing a second metal in said layer, said second metal having a metal work function, said second metal having a concentration in said layer of between about 1E16 and 1E20 atoms/cm3 at said semiconductor interface, said concentration being sufficiently low that said second metal does not diminish said first property of said layer by more than 10%, said concentration being sufficiently high and said metal work function being within +/−0.5 eV of said semiconductor work function such that the contact is ohmic.

2. The method of claim 1 , wherein said first property is an optical property.

3. The method of claim 2 , wherein said first property is reflectivity.

4. The method of claim 3 , wherein said reflectivity is not reduced by more than 10%.

5. The method of claim 3 , wherein said reflectivity is not reduced by more than 5%.

6. The method of claim 3 , wherein said reflectivity is not reduced by more than 1%.

7. The method of claim 1 , wherein said first property is adhesion or thermal conductivity.

8. The method of claim 1 , wherein diffusing said second metal in said layer comprises depositing a first layer of said first metal on a portion of said GaN semiconductor, depositing a second layer of said second metal on said first layer, and then annealing said GaN semiconductor to cause said second metal to diffuse in said first layer.

9. The method of claim 1 , further comprising diffusing a third metal diffused in said layer in a sufficient concentration to impart a third property in said layer without significantly diminishing said first property of said layer.

10. The method of claim 1 , further comprising overlaying a second layer on said layer, said second layer comprising said second metal.

11. The method of claim 10 , further comprising overlaying a third layer on said second layer, said third layer comprising said first metal.

12. The method of claim 1 , further comprising disposing a protective layer above said layer of said first metal prior to said diffusing said second metal.

13. The method of claim 12 , wherein said protective layer is a barrier for oxygen.

14. The method of claim 12 , further comprising disposing at least one additional metal layer above said layer of said first metal and below said protective layer.

15. The method of claim 1 , wherein said first metal is selected from the group consisting of silver, gold, and aluminum, and said second metal is selected from the group consisting of, aluminum and titanium.

16. The method of claim 1 , wherein said amount equates to a layer thickness of about 20 nm to about 1000 nm.

17. The method of claim 1 , wherein said concentration is between 1E18 and 1E20 atoms/cm3.

18. The method of claim 1 , wherein said concentration is an atomic concentration of the second metal at said semiconductor interface, and a ratio of said concentration to an atomic concentration of the first metal at said semiconductor interface is within a range of 1E-7 to 5E-2.

19. The method of claim 1 , wherein said second metal has an initial concentration at said semiconductor interface before being diffused, and wherein said concentration is higher than said initial concentration.

20. The method of claim 19 , wherein said concentration is higher than said initial concentration by a factor of at least 100.

21. The method of claim 1 , wherein ohmic contact has a specific contact resistance of less than 1e-3 Ohm·cm2.