SiGe/Si-Bipolar and Quantum Well Transistors, Results and Prospects

Abstract

ABSTRACTThe quality of SiGe/Si heterodevices recently could be improved by depositing on a SiGe buffer with a Ge grading. In house MBE grown structures reached 1.5 K mobilities of 173000 cm2/Vs. Also at room temperature (RT) the mobility is up to 4 times higher than in bulk Si or SiGe. HBTs in the discussed material system can exceed performances of conventional Si-homobipolar transistors, already with relaxed design rules. I briefly review on mesa - like SiGe HBTs with high fmax and fT around 50 GHz, owing to low base sheet resistances <1Kω□. In DC-operation high gains >400 or 13 000 at RT or 77K were obtained, n - and p - channel Si, SiGe and Ge MODFETs will be presented in more detail, n- MODFETs exhibit high transconductances above 300 mS/mm at RT and almost 1000 mS/mm at 77K. Different effects will be discussed, e.g. the influence of the gate to channel distance and effects of rapid thermal activation. Si/Ge heterosystems offer exclusive properties, e.g. the same mobility in a Si - 2DEG and a Ge - 2DHG. Complementary MODFETs (CMOD) can be envisaged. Furtheron the Si/Ge system allows the monolithic integration of heterodevices with high complexity Si - ICs (heterointegration).