NMR Study of Si:As and Si:P near the metal-insulator transition.

摘要: Results of pulsed NMR measurements on the $^{29}\mathrm{Si}$ spin system in Si:As and Si:P are reported for samples spanning metal-insulator (M-I) transition. The ranges donor concentrations ${n}_{D}$ 1.6\ifmmode\times\else\texttimes\fi{}${10}^{18}$ to 4\ifmmode\times\else\texttimes\fi{}${10}^{19}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ 1.1\ifmmode\times\else\texttimes\fi{}${10}^{17}$ 6.9\ifmmode\times\else\texttimes\fi{}${10}^{19}$ Si:P. measurements, made at 4.3 K primarily a resonant field 58.5 kG, show that nonzero values peak Knight shifts Korringa-like relaxation observed ${n}_{D}$/${n}_{c}$ as low 0.4. Knight-shift distributions given value appear coincide near ${10}^{20}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$, but differ respective critical two systems. Values local change smoothly through M-I determine inhomogeneous linewidth. Spin-echo give determination homogeneous, dipolar width. nuclear does not relax with single ${T}_{1}$. Interpretation data emphasizes importance focusing attention distribution shift ${T}_{1}$ this disordered system, rather than attempting characterize or