SiGe Heterobipolar Transistors Research Articles

Molecular-beam epitaxy of strained silicon germanium/silicon structures

The growth of strained layer heterostructures is influenced by intentionally undesired phenomena as surface undulations, alloy clustering, defect generation, interface intermixing. The origin of these effects is explained and strategies to overcome them are discussed. Recently, in the silicon germanium (SiGe) system exciting progress toward layers controlled on a monolayer scale was obtained. The status will be demonstrated by doped and undoped heterostructures, multiple heterostructures, and superlattices. Special emphasis will be given to structures relevant for devices as heterobipolar transistors (HBT), modulation doped field effect transistors (MODFET), and novel optoelectronic devices. For all these structures the strain is explicitly utilized for band structure engineering. In several areas the progress in material preparation pushed an tremendous performance increase. Examples given are the low base sheet resistivity (1.6 kΩ/⧠) for high speed (42 GHz) SiGe–HBTs, the 4.2 K mobility increase in n-MODFET channels to 160 000 cm2/V s, and the luminescence from various strained SiGe structures.