Theory of polarization dependent intersubband transitions in p-type SiGe/Si self-assembled quantum dots

Electronic and optoelectronic properties of SiGe/Si self-assembled quantum dots are calculated by the eight-band k.p method with a revised set of parameters. The model confirms that the Si1-xGex transforms to a type-II structure when x is greater than 0.25 and given accurate effective masses for Si and Ge. The polarization dependent absorption spectra show a behavior quite different from what is seen in conduction band intersubband transitions in self-assembled InGaAs/GaAs dots. In-plane or x-polarized absorption increases as germanium content is increased but z-polarized absorption is highest for low germanium content. It is also shown that the z-polarized absorption can be of the same magnitude as in the x-direction by adjusting the dot composition. We also clarify how the envelope functions and the Block parts of the electronic states contribute to the absorption spectra. (C) 2004 American Institute of Physics.