Abstract: In an integrated heterojunction bipolar transistor (HBT) with minimized base-collector capacitance, a sub-collector region is formed as a mesa on a substrate, a collector contact is to the sub-collector mesa region, a lightly-doped collector region and a base region extend from the mesa onto the substrate, and a base contact and its via hole for interconnection are off the mesa, with minimal overlap with the sub-collector region. The latter may be termed a buried selective sub-collector (BSSC) region. Such transistors can be used as integrated switching devices and microwave devices, e.g., in wireless communications, satellite direct broadcast systems, automobile collision avoidance systems, global positioning systems, and other high-frequency applications.

Abstract: An HBT device having heterostructure ballasting emitter is disclosed. The heterostructure ballasting emitter includes an n-type emitter setback layer on a base layer and a wide-gap ballasting emitter layer on the setback layer. The heterostructure ballasting emitter is made so that the band gap of the emitter setback layer is equal to or larger than that of the base layer and the band gap of the ballasting emitter layer is larger than that of the emitter setback layer. The heterostructure of the emitter setback layer and the ballasting emitter layer serves as the ballast. By changing the value of the valance offset between the emitter setback layer and the ballasting emitter layer, the temperature dependence of the current gain becomes adjustable. As a consequence, the present invention overcomes hurdles posed by the current gain collapse and a negative differential resistance and improves the use of the HBTs in microwave power applications.