Abstract: A bipolar transistor of the present invention comprises a collector layer made of an n-type semiconductor and an emitter layer made of an n-type semiconductor provided on this collector layer. A gate layer for injecting p-type carriers (holes) into the emitter layer is provided on the emitter layer. A p-type carrier retaining layer is formed between the collector layer and the emitter layer. The p-type carrier retaining layer temporarily retains the p-type carriers that are injected from the gate layer into the emitter layer and diffused in the emitter layer and reach the p-type carrier retaining layer. The bipolar transistor has a structure whose performance is not influenced by sheet resistance of the base layer, and is able to exhibit a high current gain even in a high-frequency region.

Abstract: A heterojunction bipolar transistor has a stack comprised of a base layer, an emitter layer and a ballast layer made of AlGaAs. The emitter layer is comprised of a single layer or a multiplicity of layers, and at least one of which is comprised of a material that prevents hole injection from the base layer into the ballast layer. Thus, the hole injection from the base layer into the emitter layer is prevented. Accordingly, it is able to prevent the conductivity modulation of the ballast layer that is the cause of a deterioration in temperature characteristics.

Abstract: A heterojunction bipolar transferred electron tetrode has an anode region providing a first terminal, an active region in which Gunn-Hilsum oscillations are generated, a base region providing a second terminal, a cathode region providing a third terminal, and a fourth terminal which is operable independently of the three terminals. The fourth terminal can take the form of a second cathode-type structure, a second base region or a Schottky gate electrode. The cathode region and fourth terminal are in proximity enough to each other such that one of the cathode region and the fourth terminal is usable as an input terminal and that the other of the cathode region and the fourth terminal is usable as a terminal to which an electrical signal for disturbing an electric field profile or a current density in the active region is applied.

Abstract: A hetero junction bipolar transistor has an emitter region, a base region, a collector region and a subcollector region which are serially arranged. The collector region includes a plurality of sub-regions. An energy bandgap in each of the sub-regions is constant or linearly changes, and an energy band edge where mobile charge carriers run in the collector region is continuous at each boundary between the sub-regions. Two-dimensional or quasi-two-dimensional charge layer is formed at the boundary of the sub-regions so as to compensate quasi-electric field caused by differences in electron affinity and energy bandgap between the sub-regions. The mobile charge carriers pass through the collector region from the base region without encountering barriers and thereby this heterojunction bipolar transistor achieves a high operating efficiency.

Abstract: A heterojunction bipolar transferred electron tetrode has an anode region providing a first terminal, an active region in which Gunn-Hilsum oscillations are generated, a base region providing a second terminal, a cathode region providing a third terminal, and a fourth terminal which is operable independently of the three terminals. The fourth terminal can take the form of a second cathode-type structure, a second base region or a Schottky gate electrode. The cathode region and fourth terminal are in proximity enough to each other such that one of the cathode region and the fourth terminal is usable as an input terminal and that the other of the cathode region and the fourth terminal is usable as a terminal to which an electrical signal for disturbing an electric field profile or a current density in the active region is applied.

Abstract: A semiconductor device for milliwave band oscillation has a Gunn diode and a Schottky diode epitaxially formed on a same substrate and connected by a transmission line. The Gunn diode is provided with an anode-ohmic electrode and a cathode-ohmic electrode. The Schottky diode is provided with a Schottky electrode formed on an active layer of n-GaAs and an ohmic electrode formed on an ohmic electrode forming high-density layer. Formation of the Schottky electrode on the active layer having a low carrier density makes it possible not only to satisfactorily obtain the Schottky characteristic of the Schottky electrode but also to require no annealing at a high temperature after ion implantation for forming other active devices. Thus, epitaxial structure deterioration and contact resistance deterioration of the semiconductor device are prevented.

Abstract: A compound semiconductor device includes a contact structure having a plurality of layers provided on a compound semiconductor layer and an electrode provided on the contact structure. The contact structure includes a first contact layer made of In.sub.x Ga.sub.1-x As (0.9.ltoreq.x.ltoreq.1) on the side closest to the electrode.

Abstract: A Gunn diode includes a layered structure including at least a cathode layer, an anode layer, and an active region interposed between the cathode and anode layers, wherein at least a portion of the active region is an AlGaAs layer.

Abstract: An ohmic electrode structure is produced by developing an In.sub.x Ga.sub.1-x As layer epitaxially on a compound semiconductor (n-Ga As), and providing a barrier layer composed of a tungsten nitride (high melting point metallic nitride) by sputtering. Then, electrode patterning is performed on the top of the tungsten nitride barrier layer by the photo-resist technique. After the process, unnecessary portion of the tungsten nitride barrier layer is removed by the reactive ion etching (RIE). On the top of this a Ti layer, a Pt layer and an Au layer are deposited in layers in that order by the lift-off technique to form a metal layer. Here, molybdenum nitride or titanium nitride may be used in place of tungsten nitride.

Abstract: A heterojunction type AlGaAs/GaAs bipolar transistor includes an n-GaAs collector layer, a p.sup.+ -GaAs base layer and an n-Al.sub.x Ga.sub.1-x As emitter layer formed in a stack, and an n-Al.sub.y Ga.sub.1-y As ballast resistance layer formed on the emitter layer. The ballast resistance layer has an Al concentration y in the range of 0<y<0.4, and a resistance higher than that of the emitter layer.

Abstract: A hetero-junction bipolar transistor includes: a substrate; a first conductive type collector layer disposed on the substrate; a second conductive type base layer having an external base region; and a first conductive type emitter layer having a bandgap larger than the bandgap of the base layer disposed in this order, wherein the emitter layer includes a first emitter layer, an etching stop layer, and a second emitter layer disposed in this order starting from the substrate side; a base electrode is formed on the etching stop layer or the first emitter layer disposed on the external base region; a region of the first emitter layer on the base layer has a thickness such that the region is substantially depleted at all voltages applied when the transistor is normally operated; the second emitter layer has an electron affinity equal to or smaller than an electron affinity of the first emitter layer; and the etching stop layer has an electron affinity larger than the electron affinity of the first emitter layer,