Compound semiconductor device having nonalloyed ohmic contacts

Claim 2

A compound semiconductor device having nonalloyed ohmic contacts comprising a compound semiconductor substrate (11); an active layer made (12) of a first semiconductor being formed on the compound semiconductor substrate, the active layer (12) having a channel region and source and drain regions; an electron supply layer (13) made of a second semiconductor being formed on the active layer (12), an electron affinity of the second semiconductor being smaller than that of the first semiconductor; an intermediate layer (14) made of a third semiconductor being formed on the electron supply layer (13) and over the source and drain regions; and a Schottky gate electrode (19G) being formed on the electron supply layer (13), characterized in that the compound semiconductor device comprises an ohmic contact layer (15) made of a fourth semiconductor which is formed on the intermediate layer (14) and makes a nonalloyed ohmic contact with metal; and source and drain electrodes (19S, 19D) formed on the ohmic contact layer (15) and over the source and drain regions.

Claim 3

A compound semiconductor device having nonalloyed ohmic contacts as claimed in claim 1, characterized in that the fourth semiconductor forming the ohmic contact layer (15) is selected from the group consisting of indium gallium arsenic (In x Ga 1-x As; 0 ≦ x ≦1) and germanium (Ge).

Claim 4

A compound semiconductor device having nonalloyed ohmic contacts as claimed in claim 2, characterized in that a doping concentration of In x Ga 1-x As is 5 × 10¹⁸ (cm⁻³) or over.

Claim 5

A compound semiconductor device having nonalloyed ohmic contacts as claimed in claim 2, characterized in that the ohmic contact layer (15) includes a graded layer portion in which the mole fraction x in In x Ga 1-x As increases from an interface with the intermediate layer (14).

Claim 6

A compound semiconductor device having nonalloyed ohmic contacts as claimed in claim 1, characterized in that the source, drain and gate electrodes (19S, 19D, 19G) are made of a same metallic substance.

Claim 7

A compound semiconductor device having nonalloyed ohmic contacts as claimed in claim 1, characterized in that a resistance of a structure comprising the active layer (12), the electron supply layer (13) and the intermediate layer (14) below the source and drain electrodes (19S, 19D) is 1 × 10⁻⁶ (Ω·cm²) or less, by selecting a mole fraction of the second semiconductor forming the electron supply layer (13).

Claim 8

A compound semiconductor device having nonalloyed ohmic contacts as claimed in claim 1, characterized in that a contact resistance of a barrier formed at an interface between the source or drain electrode (19S, 19D) and the ohmic contact layer (15) is 1 × 10⁻⁶ (Ω·cm²) or less.

Claim 9

A compound semiconductor device having nonalloyed ohmic contacts as claimed in claim 1, characterized in that a resistance of a structure comprising the active layer (12), the electron supply layer (13) and the intermediate layer (14) below the source and drain electrodes (19S, 19D) is less than that of a Schottky barrier formed below the gate electrode (19G).

Claim 10

A compound semiconductor device having nonalloyed ohmic contacts as claimed in claim 1, characterized in that the second semiconductor forming the the electron supply layer (13) is selected from the group consisting of aluminum gallium arsenic (AlGaAs), indium aluminum arsenic (InAlAs) and indium gallium phosphorus (InGaP).

Claim 11

A compound semiconductor device having nonalloyed ohmic contacts comprising a compound semiconductor substrate (11); an active layer (12) made of a first semiconductor being formed on the compound semiconductor substrate (11), the active layer (12) having a channel region and source and drain regions; an electron supply layer (13) made of a second semiconductor being formed on the active layer (12), an electron affinity of the second semiconductor being smaller than that of the first semiconductor; an intermediate layer (14) made of a third semiconductor being formed on the electron supply layer (13) and over the source and drain regions; and a Schottky gate electrode (19G) being formed on the electron supply layer (13), characterized in that the compound semiconductor device comprises an ohmic contact layer (15) made of a fourth semiconductor which is formed on the intermediate layer (14) and forms a nonalloyed ohmic contact with metal; source and drain electrodes (19S, 19D) formed on the ohmic contact layer (15) and over the source and drain regions; and a metallic layer (65) for connecting the gate electrode (19G) to at least one of the source and drain electrodes (19S, 19D) to form a logic circuit, and in that the electrodes (19S, 19D, 19G) and the metallic layer (65) are integrally formed with each other by a same metallic substance.

Claim 12

A compound semiconductor device having nonalloyed ohmic contacts comprising a compound semiconductor substrate (11); an active layer (12) made of a first semiconductor being formed on the compound semiconductor substrate (11), the active layer (12) having a channel region and source and drain regions; an electron supply layer (13) made of a second semiconductor being formed on the active layer (12), an electron affinity of the second semiconductor being smaller than that of the first semiconductor; an intermediate layer (14) made of a third semiconductor being formed on the electron supply layer (13) and over the source and drain regions; and a Schottky gate electrode (19G) being formed on the electron supply layer (13), characterized in that the compound semiconductor device comprises an ohmic contact layer (15) made of a fourth semiconductor which is formed on the intermediate layer (14) and forms a nonalloyed ohmic contact with metal; source and drain electrodes (19S, 19D) formed on the ohmic contact layer (15) and over the source and drain regions; and a metallic layer (65) for connecting the gate electrode (19G) to at least one of the source and drain electrodes (19S, 19D) to form a logic circuit, and in that the electrodes (19S, 19D, 19G) and the metallic layer (65) are integrally formed with each other by a same metallic substance.

Claim 13

A compound semiconductor device having nonalloyed ohmic contacts as claimed in claim 10, characterized in that the fourth semiconductor forming the ohmic contact layer (15) is selected from the group consisting of indium gallium arsenic (In x Ga 1-x As; 0 ≦ x ≦1) and germanium (Ge).

Claim 14

A compound semiconductor device having nonalloyed ohmic contacts as claimed in claim 11, characterized in that a doping concentration of In x Ga 1-x As is 5 × 10¹⁸ (cm⁻³) or over.

Claim 15

A compound semiconductor device having nonalloyed ohmic contacts as claimed in claim 11, characterized in that the ohmic contact layer (15) includes a graded layer portion in which the mole fraction x in In x Ga 1-x As increases from an interface with the intermediate layer.

Claim 16

A compound semiconductor device having nonalloyed ohmic contacts as claimed in claim 10, characterized in that a resistance of a structure comprising the active layer (12), the electron supply layer (13) and the intermediate layer (14) below the source and drain electrodes (19S, 19D) is 1 × 10⁻⁶ (Ω·cm²) or less, by selecting a mole fraction of the second semiconductor forming the electron supply layer (13).

Claim 17

A compound semiconductor device having nonalloyed ohmic contacts comprising a compound semiconductor substrate (21); an active layer (22) made of a first semiconductor being formed on the compound semiconductor substrate (21), the active layer (22) having a channel region and source and drain regions; and a Schottky gate electrode (26G) being formed on the active layer (22) and over the channel region formed therein, characterized in that the compound semiconductor device comprises an ohmic contact layer (24) made of a second semiconductor which is formed on portions of the active layer (22) over the source and drain regions and which makes a nonalloyed ohmic contact with metal; source and drain electrodes (26S, 26D) formed on the ohmic contact layer (24) and over the source and drain regions; and a metallic layer (65) for connecting at least one of the source and drain electrodes (26S, 26D) and the gate electrode (26G), and in that wherein the electrodes (26S, 26D) and the metallic layer (65) are integrally formed with a same metallic substance.

Claim 18

A compound semiconductor device having nonalloyed ohmic contacts comprising a compound semiconductor substrate (21); an active layer (22) made of a first semiconductor being formed on the compound semiconductor substrate (21), the active layer (22) having a channel region and source and drain regions; and a Schottky gate electrode (26G) being formed on the active layer (22) and over the channel region formed therein, characterized in that the compound semiconductor device comprises an ohmic contact layer (24) made of a second semiconductor which is formed on portions of the active layer (22) over the source and drain regions and which makes a nonalloyed ohmic contact with metal; source and drain electrodes (26S, 26D) formed on the ohmic contact layer (24) and over the source and drain regions; and a metallic layer (65) for connecting at least one of the source and drain electrodes (26S, 26D) and the gate electrode (26G), and in that wherein the electrodes (26S, 26D) and the metallic layer (65) are integrally formed with a same metallic substance.

Claim 19

A compound semiconductor device having nonalloyed ohmic contacts as claimed in claim 15, characterized in that the fourth semiconductor forming the ohmic contact layer (24) is selected from the group consisting of indium gallium arsenic (In x Ga 1-x As; 0 ≦ x ≦1) and germanium (Ge).

Claim 20

A compound semiconductor device having nonalloyed ohmic contacts as claimed in claim 16, characterized in that a doping concentration of In x Ga 1-x As is 5 × 10¹⁸ (cm⁻³) or over.

Claim 21

A compound semiconductor device having nonalloyed ohmic contacts as claimed in claim 16, characterized in that the ohmic contact layer (24) includes a graded layer portion in which the mole fraction x in In x Ga 1-x As increases from an interface with the intermediate layer.