SiGe nanostructures: new insights into growth processes

During the last decade, Si/Si1-xGex heterostructures have emerged as a viable system for use in CMOS technology with the recent industrial production of heterojunction bipolar transistor-based integrated circuits. However, many key problems have to be solved to further expand the capabilities of this system to other more attractive devices. This paper gives a comprehensive review of the progress achieved during the last few years in the understanding of some fundamental growth mechanisms. The discrepancies between classical theories (in the framework of continuum elasticity) and experimental results are also specially addressed. In. particular, the major role played by kinetics in the morphological evolution of layers is particularly emphasized. Starting from the unexpected differences in Si1-xGex morphological evolution when deposited on (001) and on (111), our review then focuses on: (1) the strain control and adjustment (from fully strained to fully relaxed 2D and 3D nanostructures)in particular, some original examples of local CBED stress measurements are presented; (2) the nucleation, growth, and self-assembly processes, using self-patterned template layers and surfactant-mediated growth; (3) the doping processes (using B for type p and Sb for type n) and the limitations induced by dopant redistribution during and after growth due to diffusion, segregation, and desorption. The final section will briefly address some relevant optical properties of Si1-xGex strained layers using special growth processes.