Thermal relaxation processes probed by intersubband and inter-valence-bandtransitions in Si/Si1-xGex multiple quantum wells

Thermal relaxation processes due to strain relaxation and Si/Ge interdiffus ion were investigated in pseudomorphic p-type SiGe/Si quantum wells using i nfrared-polarization-resolved absorption spectroscopy. The samples were ann ealed from room temperature up to 1060 degrees C and intersubband transitio ns between the lowest heavy-hole states and inter-valence-band transitions between heavy-hole and spin-split-off hole states were utilized to probe th ermal activation processes. The strain relaxation process is activated at t emperatures above 750 degrees C and causes a decrease of the intersubband a bsorption and an increase of the inter-valence-band absorption. At temperat ures above 940 degrees C, we found that a second process of Si/Ge interdiff usion causes a reduction of all absorption lines in the spectrum. We propos ed a simple model that provides a qualitative explanation to the above resu lts. (C) 1999 American Institute of Physics. [S0003-6951(99)00641-5].