In 1947, the first transistor, a bipolar junction transistor (BJT), was invented in the Bell Laboratory and has since led to the age of information technology. In recent decades, there has been a persistent demand for higher frequency operation for a BJT, leading to the inventions of new devices such as heterojunction bipolar transistors (HBT) and hot electron transistors (HET). The HBTs have enabled terahertz operations, but their cut-off frequency is ultimately limited by the base transit time; for the HETs, the demand of a thin base without pinholes and with a low base resistance usually causes difficulties in material selection and fabrication.
Click here for original story, Researchers build a silicon-graphene-germanium transistor for future THz operation
Source: Phys.org