Self aligned Si/SiGe heterojunction bipolar transistors grown by molecular beam epitaxy on diffused n+-buried layer structures

Si/SiGe heterojunction bipolar transistors (HBT´s) were fabricated and characterized. For the first time the layer sequence was deposited by low temperature silicon molecular beam epitaxy (MBE) on locally diffused buried layer structures. To improve the unfavourable ratio between the active transistor area and the inactive base area, self aligned emitter base configuration was introduced for the first time. As a main consequence the power gain cut off frequency was improved. A maximum transit frequency of ft=14GHz and a maximum frequency of oszillation of fmax = 18GHz were measured.