High-temperature elastic moduli of bulk nanostructured n- and p-type silicon germanium

Resonant ultrasound spectroscopy (RUS) has been used to measure the elastic moduli of n- and p-type doped polycrystalline bulk nanostructured silicon germanium alloys at elevated temperatures. A direct contact RUS transducer system with a working temperature range up to 900 K was successfully constructed for these measurements. For higher temperatures (up to 1300 K), we employed a traditional buffer rod RUS system. Experimental results show the Young's and shear moduli of p-type SiGe alloys monotonically decrease with increasing temperatures in the 300-1200 K range. The n-type samples show a marked stiffening beginning at 675 K which does not repeat upon cooling or subsequent reheating. We attribute the stiffening of the n-type samples to the thermally activated precipitation of the phosphorous dopant. Electrical resistivity and Seebeck coefficient data are also presented for both types of SiGe which support this conclusion.