A device includes a substrate, a drift region in the substrate, a base region above the drift region; a first high concentration region selectively formed in a part on a surface side of the base region and having a concentration higher than the drift region; a trench portion formed in a front surface of the substrate and including extending portions; and mesa portions between the extending portions. The mesa portions includes first mesa portions having the first high concentration region and second mesa portions not having the first high concentration region, the trench portion includes a first trench portion having an first conductive portion (a gate conductive portion) and adjacent to the first mesa portion, a second trench portion having the first conductive portion and adjacent to the second mesa portion, and a third trench portion having an second conductive portion and adjacent to the first or second mesa portion.

A power amplifier comprising amplifier circuits of multiple stages. Each of the amplifier circuits of multiple stages includes a bipolar transistor and a base electrode. The bipolar transistor included in each of the amplifier circuits of multiple stages includes a collector layer, a base layer placed on the collector layer, and an emitter mesa placed on part of the region of the base layer. The emitter mesa has a shape elongated in one direction in plan view. The base electrode includes a base main portion arranged in such a manner as to be separated from the emitter mesa with a gap in a direction orthogonal to a lengthwise direction of the emitter mesa in plan view. The base main portion has a shape elongated in a direction parallel to the lengthwise direction of the emitter mesa in plan view and is electrically connected to the base layer.

The present disclosure generally relates to semiconductor processing including facet trapping for an epitaxial growth process. In an example, a semiconductor device includes a first semiconductor material, a dielectric layer, and a second semiconductor material. The first semiconductor material includes a monocrystalline surface. The dielectric layer is over the first semiconductor material. The dielectric layer has an opening to the monocrystalline surface. The opening is defined at least in part by a sidewall of the dielectric layer and a cavity in the dielectric layer. The cavity is at the monocrystalline surface and under the sidewall. The second semiconductor material is over the first semiconductor material and on the monocrystalline surface. The second semiconductor material is at least partially in the opening through the dielectric layer. The cavity in the dielectric layer is configured to trap a facet of the second semiconductor material in the cavity.

In a method of forming a bipolar junction transistor (BJT) structure, an emitter/base/collector structure is formed, comprising mutually parallel fins with an insulator material disposed between the fins. Each fin of the emitter/base/collector structure has first and second peripheral regions doped with a first doping type on opposite sides of a central region doped with a second doping type opposite the first doping type. The first peripheral regions of the fins are an emitter of the BJT structure, the central regions of the fins are a base of the BJT structure, and the second peripheral regions of the fins are a collector of the BJT structure. Continuous emitter, base, and collector contact strips are epitaxially deposited on the emitter, base, and collector of the BJT structure, respectively.