Microwave conductivity and conduction-electron spin-resonance linewidth of heavily doped Si: P and Si: As

Abstract

Results are presented of a conduction-electron spin-resonance (CESR) study of single-crystal samples of heavily doped Si: P and Si: As. By studying the CESR line shape for samples whose thickness is comparable to the skin depth, we are able to deduce the microwave conductivity $\mathrm{Re}\ensuremath{\sigma}(\ensuremath{\omega})$. We find in Si: P that $\mathrm{Re}\ensuremath{\sigma}(\ensuremath{\omega})$ is less than the dc conductivity $\ensuremath{\sigma}(0)$ by a factor \ensuremath{\approx} 3 at 4.2 K for samples just below the metal-insulator transition, while above the transition $\mathrm{Re}\ensuremath{\sigma}(\ensuremath{\omega})=\ensuremath{\sigma}(0)$. We also compare the CESR linewidths for Si: P and Si: As and find large differences which imply, contrary to many previous studies, that Elliott-Yafet relaxation via spin-orbit coupling to the host is not involved. We propose that spin-orbit coupling to the impurities is the controlling factor.