Carrier-doping effect on strength and deformations in group-IV crystals

Abstract

Understanding the mechanical properties of semiconductor materials in carrier-rich environments is crucial for ensuring the reliability of devices operating under such conditions. This study examines the impact of excess carrier doping on the ideal tensile and shear strengths of Si, 3C-SiC, and diamond through first-principles calculations. High electron doping density (5.0 × 10²¹ cm⁻³) significantly reduces ideal tensile strength by approximately 60 %, 20 %, and 40 % in Si, 3C-SiC, and diamond, respectively, while hole doping enhances it by 28 %, 30 %, and 7 %. Crystal orbital Hamilton population analysis could not fully explain the strength modification mechanism in diamond as consistently as in Si and 3C-SiC. Alternatively, these effects can be understood through modifications in the interaction forces between neighboring atoms, driven by changes in charge distribution. For shear deformation along the $\left[11\overline{2}\right]$ direction, electron doping increases shear strength by approximately 10 % in Si and 3C-SiC but decreases it by 5 % in diamond, owing to structural instability under high shear. Conversely, hole doping decreases shear strength in Si and 3C-SiC but slightly increases it in diamond. In the [$\overline{1}\overline{1}2$] direction, electron doping decreases shear strength by up to 20 % in all materials, whereas hole doping decreases it by 30 % in Si and has minimal effects on 3C-SiC and diamond. The effects of excess carriers on ideal shear strength can also be interpreted through alterations in the resistive forces between the bonds. These findings suggest that excess carriers modify mechanical properties by altering charge density distribution, affecting bond repulsion and deformation resistance.