Abstract: This composite semiconductor device has a normally-on first field effect transistor and a normally-off second field effect transistor connected in series between first and second terminals, gates of the first and second field effect transistors being connected to second and third terminals, respectively, and N diodes being connected in series in a forward direction between a drain and a source of the second field effect transistor. Therefore, a drain-source voltage (Vds) of the second field effect transistor can be restricted to a voltage not higher than a withstand voltage of the second field effect transistor.

Abstract: This composite semiconductor device has a normally-on first field effect transistor and a normally-off second field effect transistor connected in series between first and second terminals, gates of the first and second field effect transistors being connected to second and third terminals, respectively, and N diodes being connected in series in a forward direction between a drain and a source of the second field effect transistor. Therefore, a drain-source voltage (Vds) of the second field effect transistor can be restricted to a voltage not higher than a withstand voltage of the second field effect transistor.

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: The present invention provides a heterojunction bipolar transister includes: a collector layer, a base layer, an emitter layer, a transition layer formed between the base layer and the emitter layer, a collector electrode connected to the collector layer, a base electrode connected to the base layer, and an emitter electrode connected to the emitter layer, wherein the emitter layer and the transition layer are formed of a composition including elements forming the base layer and at least one element different from the elements forming the base layer, a composition of the different element in the transition layer at the emitter side is substantially equal to that of the emitter layer, a composition of the different element in the transition layer at the base side is smaller than that of the emitter side and varies abruptly towards the base layer, and the composition of the transition layer gradingly varies from the base side to the emitter side.

Abstract: An electric-signal amplifying device is provided which includes a light source and an opto-electronic element for amplifying an input signal by use of light emitted from the light source. The opto-electronic element includes a semiconductor substrate and a multi-layered structure disposed thereon. The multi-layered structure has a first semiconductor layer of a first conductivity type, a second semiconductor layer of a second conductivity type, and a third semi-conductor layer of the first conductivity type in this order. The second and third semiconductor layers form a first p-n junction for modulating the amount of light to be absorbed thereinto with a change of bias voltage applied thereto in accordance with the input signal, while the first and second semiconductor layers form a second p-n junction for generating a current as an amplified output signal by absorption of the light transmitted through the first p-n junction.