Nitride based transistors on semi-insulating silicon carbide substrates

Claim 2

A high electron mobility transistor (HEMT) comprising: a semi-insulating substrate ( 1 ); an aluminum nitride buffer layer ( 12 ) on said substrate; and an insulating gallium nitride layer ( 13 ) on said buffer layer; and characterized by an active structure ( 14 ) of aluminum gallium nitride on said gallium nitride layer; respective source, drain, and gate contacts ( 20 , 21 , 22 ) to said aluminum gallium nitride active structure, and a passivation layer ( 23 ) for enhancing the flow of electrons in said active structure, said passivation layer being selected from the group consisting of silicon dioxide and silicon nitride on said aluminum gallium nitride active structure, said passivation layer covering contact portions of the source, drain and gate contacts and possessing windows to permit electrical connections to said source, gate and drain contacts.

Claim 3

A HEMT according to claim 1 wherein said aluminum gallium nitride active structure ( 14 ) comprises: a first undoped aluminum gallium nitride layer ( 15 ) on said gallium nitride insulating layer; a conductively doped aluminum gallium nitride layer ( 16 ) on said undoped aluminum nitride layer, and a second undoped aluminum gallium nitride layer ( 17 ) on said conductivity doped aluminum nitride layer.

Claim 4

A HEMT according to claim 2 wherein: said passivation layer is on said second undoped aluminum nitride layer; said conductivity doped aluminum gallium nitride layer ( 16 ) is replaced with an undoped layer of aluminum gallium nitride.

Claim 5

A HEMT according to claim 1 wherein said substrate comprises the 4H polytype of silicon carbide and has a bulk resistivity higher than 10 5 Ω-cm.

Claim 6

A HEMT according to claim 1 wherein: said source and drain contacts comprise an alloy of titanium, aluminum, and nickel, or on alloy of titanium, silicon, and nickel; and said gate contact is selected from the group consisting of titanium, platinum, chromium, alloys of titanium and tungsten, and platinum silicide.

Claim 7

A high electron mobility transistor (HEMT) comprising: a semi-insulating substrate ( 11 ); and characterized by a heterojunction structure between two different group III nitride semiconductor materials wherein said heterojunction comprises adjacent layers of aluminum gallium nitride ( 14 ) and gallium nitride ( 13 ); contacts ( 20 , 22 , 21 ) to said heterojunction materials to define respective source, gate and drain portions of said transistor; and a passivation layer ( 23 ), for enhancing the flow of electrons in said active structure, selected from the group consisting of silicon nitride and silicon dioxide covering the top surface of said heterojunction materials and covering at least portions of said contacts.

Claim 8

A high electron mobility transistor (HEMT) comprising: a semi-insulating substrate ( 11 ); and characterized by a heterojunction structure between two different group III nitride semiconductor materials wherein said heterojunction comprises adjacent layers of aluminum gallium nitride ( 14 ) and gallium nitride ( 13 ); contacts ( 20 , 22 , 21 ) to said heterojunction materials to define respective source, gate and drain portions of said transistor; and a passivation layer ( 23 ), for enhancing the flow of electrons in said active structure, selected from the group consisting of silicon nitride and silicon dioxide covering the top surface of said heterojunction materials and covering at least portions of said contacts.

Claim 9

A HEMT according to claim 6 : further comprising an aluminum nitride buffer layer ( 12 ) between said substrate and said heterojunction structure.

Claim 10

A HEMT according to claim 7 and wherein: said gallium nitride layer is undoped; and said aluminum gallium nitride layer ( 14 ) is formed of a first undoped (layer of AlGaN ( 15 ) on said gallium nitride layer; a donor-doped layer of AlGaN (l 6 ) on said first undoped AlGaN layer; and a second undoped AlGaN layer ( 17 ) on said donor-doped AlGaN layer.

Claim 11

A HEMT according to claim 8 wherein all three of said AlGaN layers have the same male fraction of Al and Ga.

Claim 12

A HEMT according to claim 8 wherein at least two of said three AlGaN layers have different mole fractions of Al and Ga.

Claim 13

A HEMT according to claim 7 wherein said aluminum nitride buffer layer is on said substrate and said gallium nitride layer is on said buffer layer.

Claim 14

A HEMT according to claim 6 wherein: said contacts defining said source and drain portions of said transistor comprise on alloy of titanium, aluminum, and nickel, or an alloy of titanium, silicon, and nickel; and said contact defining said gate portion of said transistor is selected from the group consisting of titanium, platinum, chromium, alloys of titanium and tungsten, and platinum silicide.

Claim 15

A HEMT according to claim 6 wherein said semi-insulating substrate comprises silicon carbide.

Claim 16

A high electron mobility transistor (HEMT) comprising: a semi-insulating substrate ( 1 ); an aluminum nitride buffer layer ( 12 ) on said substrate; and an insulating gallium nitride layer ( 13 ) on said buffer layer; and characterized by an active structure ( 14 ) of aluminum gallium nitride on said gallium nitride layer, wherein said aluminum gallium nitride active structure comprises: a first undoped aluminum gallium nitride layer ( 15 ) on said gallium nitride insulating layer; a conductively doped aluminum gallium nitride layer ( 16 ) on said undoped aluminum nitride layer; and a second undoped aluminum gallium nitride layer ( 17 ) on said conductively doped aluminum nitride layer; respective source, drain, and gate contacts ( 20 , 21 , 22 ) to said aluminum gallium nitride active structure, and a passivation layer ( 23 ) selected from the group consisting of silicon dioxide and silicon nitride on said aluminum gallium nitride active structure, said passivation layer covering contact portions of the source, drain and gate contacts pad processing windows to permit electrical connections to said source, gate and drain contacts.

Claim 17

A high electron mobility transistor (HEMT) comprising: a semi-insulating substrate ( 1 ); an aluminum nitride buffer layer ( 12 ) on said substrate; and an insulating gallium nitride layer ( 13 ) on said buffer layer; and characterized by an active structure ( 14 ) of aluminum gallium nitride on said gallium nitride layer, wherein said aluminum gallium nitride active structure comprises: a first undoped aluminum gallium nitride layer ( 15 ) on said gallium nitride insulating layer; a conductively doped aluminum gallium nitride layer ( 16 ) on said undoped aluminum nitride layer; and a second undoped aluminum gallium nitride layer ( 17 ) on said conductively doped aluminum nitride layer; respective source, drain, and gate contacts ( 20 , 21 , 22 ) to said aluminum gallium nitride active structure, and a passivation layer ( 23 ) selected from the group consisting of silicon dioxide and silicon nitride on said aluminum gallium nitride active structure, said passivation layer covering contact portions of the source, drain and gate contacts pad processing windows to permit electrical connections to said source, gate and drain contacts.

Claim 18

A HEMT according to claim 14 wherein: said passivation layer is on said second undoped aluminum nitride layer; said conductively doped aluminum gallium nitride layer ( 16 ) is replaced with an undoped layer of aluminum nitride.

Claim 19

A high electron mobility transistor (HEMT) comprising: a semi-insulating substrate ( 11 ); and characterized by a heterojunction structure between two different group III nitride semiconductor materials wherein said heterojunction comprises adjacent layers of aluminum gallium nitride ( 14 ) and gallium nitride ( 13 ), wherein said gallium nitride layer, ( 13 ) is undoped and said aluminum gallium nitride layer ( 14 ) is formed of a first undoped layer of AlGaN ( 15 ) on said gallium nitride layer; a donor-doped layer of AlGaN ( 16 ) on said first undoped AlGaN layer, and a second undoped AlGaN layer ( 17 ) on said donor-doped AlGaN layer; and an aluminum nitride buffer layer ( 12 ) between said substrate on said heterojunction structure; contacts ( 20 , 22 , 21 ) to said heterojunction materials to define respective source, gate and drain portions of said transistor; and a passivation layer ( 23 ), selected from the group consisting of silicon nitride and silicon dioxide covering the top surface of said heterojunction materials and covering at least portions of said contacts.

Claim 20

A high electron mobility transistor (HEMT) comprising: a semi-insulating substrate ( 11 ); and characterized by a heterojunction structure between two different group III nitride semiconductor materials wherein said heterojunction comprises adjacent layers of aluminum gallium nitride ( 14 ) and gallium nitride ( 13 ), wherein said gallium nitride layer, ( 13 ) is undoped and said aluminum gallium nitride layer ( 14 ) is formed of a first undoped layer of AlGaN ( 15 ) on said gallium nitride layer; a donor-doped layer of AlGaN ( 16 ) on said first undoped AlGaN layer, and a second undoped AlGaN layer ( 17 ) on said donor-doped AlGaN layer; and an aluminum nitride buffer layer ( 12 ) between said substrate on said heterojunction structure; contacts ( 20 , 22 , 21 ) to said heterojunction materials to define respective source, gate and drain portions of said transistor; and a passivation layer ( 23 ), selected from the group consisting of silicon nitride and silicon dioxide covering the top surface of said heterojunction materials and covering at least portions of said contacts.

Claim 21

A HEMT according to claim 16 wherein all three of said AlGaN layers have the same mole fraction of Al and Ga.

Claim 22

A HEMT according to claim 16 wherein at least two of said three AlGaN layers have different mole fractions of Al and Ga.