HETEROBIPOLAR TRANSISTOR

摘要

In a heterobipolar transistor, an SiGe spacer layer (40), an SiGe graded layer (41) partly functioning as a base layer and composed of split layers of different Ge contents, and an Si cap layer (42) are formed on a collector layer (12) formed in a portion of an Si substrate (10). In the SiGe graded layer (41), as the thickness of each split layer increases, as the number of split layers decreases, and as the difference of the Ge composition between adjoining split layers increases, the measurement of the film thickness becomes easier. To avoid degradation of the device cutoff frequency, it is necessary that the thickness of each split layer is about 20 nm or less, and it is preferable that the number of split layers is two or greater.