DETAILED DESCRIPTION OF THE DRAWING The drawing is a schematic cross section of an exemplary compound semiconductor device having an improved ohmic contact in accordance with the invention.
The exemplary semiconductor device comprises a body 10 of compound semiconductor material, such as gallium arsenide, having regions of p-type conductivity 11 and n-type conductivity 12 and one or more p-n junctions 13 therebetween.
Advantageously, the active surface of the device is protected by a passivating layer 14 such as glass.
In the particular example of FIG.
1, the device is useful as a rectifying diode.
The semiconductor device includes one or more ohmic contacts generally denoted 15A and 15B, each of which comprises a layer 16 of conductive material, such as nickel, in contact with the semiconductor body and overlaying a semiconductor region of one conductivity type.
In accordance with the invention, at least one of these ohmic contacts, e.
g.
, 15A, includes, disposed between the conductive layer and the underlying semiconductor region, an intervening multiple-doped region 17 of the semiconductor body which is substantially saturated with a plurality of different impurities of the same conductivity type.
The different impurities being respectively suitable for occupying the different types of impurity sites available in the compound semiconductor.
Typically these impurities are of the same conductivity type as the dopant of the underlying semiconductor.
The net carrier concentration is the sum of the carrier concentrations of the two dopants.
In compound semiconductors having metal and non-metal components, one p-type dopant can be an element which has one less or fewer valence electrons than the non-metal component of the semiconductor for which it is substituted.
The other p-type dopant can be an element having one less or fewer valence electrons than the metal component for which it is substituted.
Thus, for example, in III-V compound semiconductors, in order to produce p-type contacts, Group IV dopants can be substituted for the Group V semiconductor atoms, and Group II dopants can be substituted for the Group III atoms
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