T_1 and T_2 spin relaxation time limitations of phosphorous donor electrons near crystalline silicon to silicon dioxide interface defects

摘要

A study of donor electron spins and spin-dependent electronic transitions involving phosphorous (~(31)P) atoms in proximity to the (111) oriented crystalline silicon (c-Si) to silicon dioxide (SiO_2) interface is presented for [~(31)P]=10~(15) cm~(-3) and [~(31)P] = 10~(16) cm~(-3) at about liquid-~4He temperatures (T=5-15 K). Using pulsed electrically detected magnetic resonance (pEDMR), spin-dependent transitions between the ~(31)P donor state and two distinguishable interface states are observed, namely, (ⅰ) P_b centers, which can be identified by their characteristic anisotropy, and (ⅱ) a more isotropic center which is attributed to E' defects of the SiO_2 bulk close to the interface. Correlation measurements of the dynamics of spin-dependent recombination confirm that previously proposed transitions between ~(31)P and the interface defects take place. The influence of these electronic near-interface transitions on the ~(31)P donor spin-coherence time T_2 as well as the donor spin-lattice relaxation time T_1 is then investigated by comparison of spin Hahn-echo decay measurements obtained from conventional bulk sensitive pulsed electron paramagnetic resonance and surface sensitive pEDMR, as well as surface sensitive electrically detected inversion recovery experiments. The measurements reveal that the T_2 times of both interface states and ~(31)P donor electron spins in proximity to them are consistently shorter than the T_1 times, and both T_2 and T_1 times of the near-interface donors are reduced by several orders of magnitude from those in the bulk, at T ≤ 13 K. The T_2 times of the ~(31)P donor electrons are in agreement with the prediction by de Sousa that they are limited by interface-defect induced field noise.