Experimental study on the effect of impurity concentration on phonon and electronic transport properties of single-crystal silicon

Abstract

Investigation of the impurity concentration dependence of phonon and electronic transports is essential for semiconductor devices requiring thermal management. However, the experimental study of phonon transport properties is limited compared to theoretical studies. Therefore, in this work, n-type single-crystal silicon with different impurity concentrations was prepared to measure group velocity and thermal conductivity using nanoindentation and spot periodic heating with infrared radiation thermometry, respectively. Phonon mean free path (MFP) was evaluated by analyzing the measured group velocity and thermal conductivity. Electron MFP was determined from thermal velocity and relaxation time based on mobility. The impurity concentration dependences of electron and phonon MFPs differed significantly. Electron MFP decreased from 53 to 4.6 nm when the impurity concentration was increased from 2.3 × 1014 to 7.0 × 1018 cm−3. In contrast, phonon MFP exhibited a constant value of approximately 36 nm for an impurity concentration ranging from 2.3 × 1014 to 1.6 × 1017 cm−3. However, upon a further increase in the impurity concentration to 7.0 × 1018 cm−3, the phonon MFP decreased to 30 nm. These findings are especially beneficial for the fabrication of high-performance nanostructured thermoelectric materials.