Abstract: A heterojunction bipolar transistor includes a collector layer, a base layer, and an emitter layer that are stacked on a substrate. The collector layer includes a graded semiconductor layer in which an electron affinity increases from a side closer to the base layer toward a side farther from the base layer. An electron affinity of the base layer at an interface closer to the collector layer is equal to an electron affinity of the graded semiconductor layer at an interface closer to the base layer.

Abstract: A semiconductor device includes a semiconductor substrate and first and second bipolar transistors. The semiconductor substrate includes first and second main surfaces opposing each other. The first bipolar transistor is formed on the first main surface of the semiconductor substrate and includes a first emitter layer. The second bipolar transistor is formed on the first main surface of the semiconductor substrate and includes a second emitter layer and a resistor layer. The resistor layer is stacked on the second emitter layer in a direction normal to the first main surface.

Abstract: A bipolar transistor includes a collector layer, a base layer, and an emitter layer that are formed in this order on a compound semiconductor substrate. The emitter layer is disposed inside an edge of the base layer in plan view. A base electrode is disposed on partial regions of the emitter layer and the base layer so as to extend from an inside of the emitter layer to an outside of the base layer in plan view. An insulating film is disposed between the base electrode and a portion of the base layer, with the portion not overlapping the emitter layer. An alloy layer extends from the base electrode through the emitter layer in a thickness direction and reaches the base layer. The alloy layer contains at least one element constituting the base electrode and elements constituting the emitter layer and the base layer.

Abstract: A semiconductor device includes a sub-collector layer disposed on a substrate, a bipolar transistor including a collector layer formed of a semiconductor having a lower carrier concentration than the sub-collector layer, a base layer, and an emitter layer, and a protection diode including a Schottky electrode. The Schottky electrode forms, in a partial region of an upper surface of the collector layer, a Schottky junction to the collector layer and is connected to one of the base layer and the emitter layer. In the collector layer, a part that forms a junction to the base layer and a part that forms a junction to the Schottky electrode are electrically connected to each other via the collector layer.

Abstract: An amplifier circuit including a semiconductor element is formed on a substrate. A protection circuit formed on the substrate includes a plurality of protection diodes that are connected in series with each other, and the protection circuit is connected to an output terminal of the amplifier circuit. A pad conductive layer at least partially includes a pad for connecting to a circuit outside the substrate. The pad conductive layer and the protection circuit at least partially overlap each other in plan view.

Abstract: A compound semiconductor substrate has a first main surface parallel to a first direction and a second direction perpendicular to the first direction, a second main surface located on a side opposite to the first main surface, and a recess. The recess has an opening, a bottom surface facing the opening, and a plurality of side surfaces located between the opening and the bottom surface. The side surfaces include at least one first side surface forming an angle of about ? degrees with the bottom surface in the recess and at least one second side surface forming an angle of about ? degrees with the bottom surface in the recess. The total length of edge lines between the first main surface and the at least one first side surface is larger than that of edge lines between the first main surface and the at least one second side surface.

Abstract: A high-performance HBT that is unlikely to decrease the process controllability and to increase the manufacturing cost is implemented. A heterojunction bipolar transistor includes an emitter layer, a base layer, and a collector layer on a GaAs substrate. The emitter layer is formed of InGaP. The base layer is formed of GaAsPBi having a composition that substantially lattice-matches GaAs.

Abstract: A collector layer of an HBT includes a high-concentration collector layer and a low-concentration collector layer thereon. The low-concentration collector layer includes a graded collector layer in which the energy band gap varies to narrow with increasing distance from the base layer. The electron affinity of the semiconductor material for the base layer is greater than that of the semiconductor material for the graded collector layer at the point of the largest energy band gap by about 0.15 eV or less. The electron velocity in the graded collector layer peaks at a certain electric field strength. In the graded collector layer, the strength of the quasi-electric field, an electric field that acts on electrons as a result of the varying energy band gap, is between about 0.3 times and about 1.8 times the peak electric field strength, the electric field strength at which the electron velocity peaks.

Abstract: A circuit element is formed on a substrate made of a compound semiconductor. A bonding pad is disposed on the circuit element so as to at least partially overlap the circuit element. The bonding pad includes a first metal film and a second metal film formed on the first metal film. A metal material of the second metal film has a higher Young's modulus than a metal material of the first metal film.

Abstract: A semiconductor device includes a semiconductor substrate and first and second bipolar transistors. The semiconductor substrate includes first and second main surfaces opposing each other. The first bipolar transistor is formed on the first main surface of the semiconductor substrate and includes a first emitter layer. The second bipolar transistor is formed on the first main surface of the semiconductor substrate and includes a second emitter layer and a resistor layer. The resistor layer is stacked on the second emitter layer in a direction normal to the first main surface.

Abstract: An amplifier circuit including a semiconductor element is formed on a substrate. A protection circuit formed on the substrate includes a plurality of protection diodes that are connected in series with each other, and the protection circuit is connected to an output terminal of the amplifier circuit. A pad conductive layer at least partially includes a pad for connecting to a circuit outside the substrate. The pad conductive layer and the protection circuit at least partially overlap each other in plan view.

Abstract: A compound semiconductor substrate has a first main surface parallel to a first direction and a second direction perpendicular to the first direction, a second main surface located on a side opposite to the first main surface, and a recess. The recess has an opening, a bottom surface facing the opening, and a plurality of side surfaces located between the opening and the bottom surface. The side surfaces include at least one first side surface forming an angle of about ? degrees with the bottom surface in the recess and at least one second side surface forming an angle of about ? degrees with the bottom surface in the recess. The total length of edge lines between the first main surface and the at least one first side surface is larger than that of edge lines between the first main surface and the at least one second side surface.

Abstract: A semiconductor chip includes a single-crystal substrate and a metal electrode on the bottom surface of the substrate. The metal electrode has a region in which a first metal is exposed and a region in which a second metal is exposed, the second metal having a standard electrode potential different from that of the first metal.

Abstract: A collector layer of an HBT includes a high-concentration collector layer and a low-concentration collector layer thereon. The low-concentration collector layer includes a graded collector layer in which the energy band gap varies to narrow with increasing distance from the base layer. The electron affinity of the semiconductor material for the base layer is greater than that of the semiconductor material for the graded collector layer at the point of the largest energy band gap by about 0.15 eV or less. The electron velocity in the graded collector layer peaks at a certain electric field strength. In the graded collector layer, the strength of the quasi-electric field, an electric field that acts on electrons as a result of the varying energy band gap, is between about 0.3 times and about 1.8 times the peak electric field strength, the electric field strength at which the electron velocity peaks.

Abstract: A collector layer of an HBT includes a high-concentration collector layer and a low-concentration collector layer thereon. The low-concentration collector layer includes a graded collector layer in which the energy band gap varies to narrow with increasing distance from the base layer. The electron affinity of the semiconductor material for the base layer is greater than that of the semiconductor material for the graded collector layer at the point of the largest energy band gap by about 0.15 eV or less. The electron velocity in the graded collector layer peaks at a certain electric field strength. In the graded collector layer, the strength of the quasi-electric field, an electric field that acts on electrons as a result of the varying energy band gap, is between about 0.3 times and about 1.8 times the peak electric field strength, the electric field strength at which the electron velocity peaks.

Abstract: A semiconductor device includes a semiconductor substrate and first and second bipolar transistors. The semiconductor substrate includes first and second main surfaces opposing each other. The first bipolar transistor is formed on the first main surface of the semiconductor substrate and includes a first emitter layer. The second bipolar transistor is formed on the first main surface of the semiconductor substrate and includes a second emitter layer and a resistor layer. The resistor layer is stacked on the second emitter layer in a direction normal to the first main surface.

Abstract: An HBT includes a semiconductor substrate having first and second principal surfaces opposite each other; and a collector layer, a base layer, and an emitter layer stacked in this order on the first principal surface side of the semiconductor substrate. The collector layer includes a first semiconductor layer with metal particles dispersed therein, the metal particles each formed by a plurality of metal atoms bonded with each other.

Abstract: A heterojunction bipolar transistor includes a collector layer, a base layer, an emitter layer, and a semiconductor layer that are laminated in this order, wherein the emitter layer includes a first region having an upper surface on which the semiconductor layer is laminated, and a second region being adjacent to the first region and having an upper surface that is exposed, and the first and second regions of the emitter layer have higher doping concentrations in portions near the upper surfaces than in portions near an interface between the emitter layer and the base layer.

Abstract: An HBT includes a semiconductor substrate having first and second principal surfaces opposite each other; and a collector layer, a base layer, and an emitter layer stacked in this order on the first principal surface side of the semiconductor substrate. The collector layer includes a first semiconductor layer with metal particles dispersed therein, the metal particles each formed by a plurality of metal atoms bonded with each other.

Abstract: A semiconductor device includes a semiconductor substrate and first and second bipolar transistors. The semiconductor substrate includes first and second main surfaces opposing each other. The first bipolar transistor is formed on the first main surface of the semiconductor substrate and includes a first emitter layer. The second bipolar transistor is formed on the first main surface of the semiconductor substrate and includes a second emitter layer and a resistor layer. The resistor layer is stacked on the second emitter layer in a direction normal to the first main surface.