Growth mechanisms in thin film epitaxy of Si/SiGe from hydrides

Epitaxial growth of Si/SiGe from hydride precursors has been well established as the preferred technique for preparation of ‘virtual substrate’ and active layers of heterojunction metal-oxide-semiconductor devices as well as other Si/SiGe heterojunction based device structures. This paper reviews briefly the role of hydrogen in the growth mechanisms and establishes the basic reaction pathways in the growth process. The surface related segregation of Ge and As are examined in the context of formation of sharp SiGe/Si heterojunctions and sharp doping profiles. The influence of the growth environment on these surface segregation processes are revealed by the extended rate equation based ‘two-site’ exchange model. The optimisation of growth conditions are clearly identified from the trend gathered from secondary ion mass spectrometry measurements. The strain relaxation process during the growth of virtual substrates often leads to bunching and a high density of threading dislocations and requires substantially thicker grading layers. Some preliminary work shows that incorporation of ‘stresser’ layers in the grading region substantially reduces these detrimental features enabling relatively thin grading layers to be used.