Ohmic Contact Technologies

        

An ohmic contact refers to the contact between a metal and a semiconductor to allow carriers to flow in and out of the semiconductor. An ideal ohmic contact must have no effect on device performance, i.e., it must be capable of delivering the required current with no voltage drop between the semiconductor and the metal. 

     

In real life, therefore, an ohmic contact must have a contact resistance that is as small as possible, to make it negligible in comparison to the bulk or spreading resistance of the semiconductor. Table 1 shows some of the ohmic contact technologies used for various semiconductors. 

                           

Table 1. Some Ohmic Contact Technologies for Various Semiconductors

Semicon-

ductor

Bandgap Energy (eV)

Type

Contact Material

Technique(s)

Alloy Temp. (deg C)

Si

1.12

n,p

CoSi2

Direct Reaction*

900

1.12

n,p

TiSi2

Direct Reaction*

900

1.12

n,p

WSi2

Direct Reaction*

1000

1.12

n,p

TaSi2

Direct Reaction*

1000

1.12

n,p

PtSi

Direct Reaction*

600-700

1.12

n,p

Al

Evaporation

-

1.12

n

Au-Sb (1% Sb)

Evaporation

-

Ge

0.66

n

Au-Sb (1% Sb)

Evaporation

-

AlN

5.9

Semi-i

Si

Preform

-

Semi-i

Al, Al-in

Preform

1500-1800

Semi-i

Mo, W

Sputter

1000

AlP

2.45

n

Ga-Ag

Preform

500-1000

AlAs

2.16

n,p

In-Te

Preform

150

n,p

Au

Preform

160

n,p

Au-Ge

Preform

700

n

Au-Sn

Preform

-

GaN

3.36

Semi-i

Al-In

Preform

-

GaP

2.26

p

Au-Zn (99:1)

Evaporation

700

p

Au-Ge

Preform

-

n

Au-Sn (62:38)

Preform

360

n

Au-Si (98:2)

Evaporation

700

GaAs

1.42

p

Au-Zn (99:1)

Electroless

600

p

In-Au (80:20)

Preform

-

n

Au-Ge (88:12)

Evaporation

-

n

In-Au (90:10)

Evaporation

350-450

n

Au-Si (94:6)

Evaporation

550

n

Au-Sn (90:10)

Evaporation

300

n

Au-Te (98:2)

Evaporation

350-700

GaSb

0.72

p

In

Preform

500

n

In

Preform

 -

InP

1.35

p

In

Preform

-

n

In, In-Te

Preform

350-600

n

Ag-Sn

Preform

350-600

n

Ag-Sn

Evaporation

600

InAs

0.36

n

In

Preform

-

n

Sn-Te (99:1)

Preform

-

InSb

0.17

n

In

Preform

-

n

Sn-Te (99:1)

Preform

-

GaAs1-xPx

1.42-2.31

p

Au-Zn

Evaporation

500

p

Al

Evaporation

500

n

Au-Ge-Ni

Evaporation

450

n

Au-Sn

Evaporation

450

AlxGa1-xAs

1.42-2.16

p

Au-In

Electroplate

400-450

p

Au-Zn

Evaporation

 -

p

Al

Evaporation

500

n

Au-Ge-Ni

Evaporation

500

n

Au-Sn

Evaporation

450-485

n

Au-Sn

Electroless

450

n

Au-Si

Evaporation

 -

Ga1-xInxSb

0.70-0.17

n

Sn-Te

Evaporation

-

AlxGa1-xP

2.31-2.45

n

Sn

Preform

-

Ga1-xInxAs

1.47-0.35

n

Sn

Preform

-

InAsxSb1-x

0.17-0.35

n

In-Te

Preform

-

*Aside from direct reaction, silicides such as PtSi, TaSi2, WSi2, TiSi2, and CoSi2 may also be deposited over silicon by co-evaporation, sputter-deposition, or CVD.

    

Reference:  Physics of Semiconductor Devices

   

   

Wafer Fab Links:  DiffusionIon ImplantThin Films Metallization

 

See also:  Silicide Formation

   

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