Integrated heterostructures of Group III-V nitride semiconductor materials including epitaxial ohmic contact non-nitride buffer layer and methods of fabricating same

An ohmic contact for a semiconductor device formed of Group III-V nitride compound semiconductor materials and including a first layer comprising aluminum nitride or aluminum gallium nitride, and which is doped a predetermined conductivity type, said ohmic contact comprising:

• a second layer comprising aluminum gallium nitride on said first layer, which is doped said predetermined conductivity type and which is continuously graded such that concentration of gallium relative to aluminum increases continuously from adjacent said first layer to opposite said first layer;
• a third layer comprising gallium nitride or an alloy thereof on said second layer, and which is doped said predetermined conductivity type;
• and
• a conductor layer on said third layer, said second layer and said third layer forming an ohmic contact between said first layer and said conductor layer.

An integrated heterostructure device of Group III-V nitride compound semiconductor materials, comprising:

• a first layer comprising a first binary Group III-V nitride compound semiconductor material or an alloy thereof, said first binary Group III-V nitride compound semiconductor material or an alloy thereof comprising a first Group III element and nitrogen, and which is doped a predetermined conductivity type;
• a second layer comprising a ternary Group III-V nitride compound semiconductor material, including said first group III element, a second Group III element and nitrogen, on said first layer, said ternary Group III nitride compound semiconductor material being doped said predetermined conductivity type and being continuously graded such that concentration of said second Group III element relative to said first Group III element increases continuously from adjacent said first layer to opposite said first layer;
• a third layer comprising a second binary Group III-V nitride compound semiconductor material or an alloy thereof, including said second Group III element and nitrogen, on said second layer, said second binary Group III-V nitride compound semiconductor material or an alloy thereof being doped said predetermined conductivity type;
• and
• a conductor layer on said third layer, said second layer and said third layer forming an ohmic contact between said first layer and said conductor layer.

An integrated heterostructure device of Group III-V nitride compound semiconductor materials, comprising:

• a first layer comprising aluminum nitride or aluminum gallium nitride, and which is doped a predetermined conductivity type;
• a second layer comprising aluminum gallium nitride on said first layer, which is doped said predetermined conductivity type and which is continuously graded such that concentration of gallium relative to aluminum increases continuously from adjacent said first layer to opposite said first layer;
• a third layer comprising gallium nitride or an alloy thereof on said second layer, and which is doped said predetermined conductivity type;
• and
• a conductor layer on said third layer, said second layer and said third layer forming an ohmic contact between said first layer and said conductor layer.

A bipolar transistor, comprising:

• a base, an emitter and a collector, each of which includes a first layer comprising a first binary Group III-V nitride compound semiconductor material or an alloy thereof, said first binary Group III-V nitride compound semiconductor material or an alloy thereof comprising a first Group III element and nitrogen;
• and
• an ohmic contact for each of said base, said emitter and said collector, each ohmic contact comprising:
• a second layer comprising a ternary Group III-V nitride compound semiconductor material, including said first group III element, a second Group III element and nitrogen, on said first layer, said ternary Group III-V nitride compound semiconductor material being continuously graded such that concentration of said second Group III element relative to said first Group III element increases continuously from adjacent said first layer to opposite said first layer;
• a third layer comprising a second binary Group III-V nitride compound semiconductor material or an alloy thereof, including said second Group III element and nitrogen, on said second layer;
• and
• a conductor layer on said third layer, said second layer and said third layer forming an ohmic contact between the respective base, emitter and collector, and the respective conductor layer.

A field effect transistor, comprising:

• spaced apart source and drain regions and a channel region therebetween;
• a gate adjacent said channel, said gate including a first layer comprising a first binary Group III-V nitride compound semiconductor material or an alloy thereof, said first binary Group III-V nitride compound semiconductor material or an alloy thereof comprising a first Group III element and nitrogen, and which is doped a predetermined conductivity type;
• and
• an ohmic contact for said gate, said ohmic contact comprising:
• a second layer comprising a ternary Group III-V nitride compound semiconductor material, including said first group III element, a second Group III element and nitrogen, on said first layer, said ternary Group III-V nitride compound semiconductor material being doped said predetermined conductivity type and being continuously graded such that concentration of said second Group III element relative to said first Group III element increases continuously from adjacent said first layer to opposite said first layer;
• a third layer comprising a second binary Group III-V nitride compound semiconductor material or an alloy thereof, including said second Group III element and nitrogen, on said second layer, said second binary Group III-V nitride compound semiconductor material or an alloy thereof being doped said predetermined conductivity type;
• and
• a conductor layer on said third layer, said second layer and said third layer forming an ohmic contact between said first layer and said conductor layer.