T1 and T2 spin relaxation time limitations of phosphorous donor electrons near crystalline silicon to silicon dioxide interface defects

A study of donor electron spins and spin-dependent electronic transitions involving phosphorous (P-31) atoms in proximity to the (111) oriented crystalline silicon (c-Si) to silicon dioxide (SiO2) interface is presented for [P-31] = 10(15) cm(-3) and [P-31] = 10(16) cm(-3) at about liquid-He-4 temperatures (T = 5-15 K). Using pulsed electrically detected magnetic resonance (pEDMR), spin-dependent transitions between the P-31 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 SiO2 bulk close to the interface. Correlation measurements of the dynamics of spin-dependent recombination confirm that previously proposed transitions between P-31 and the interface defects take place. The influence of these electronic near-interface transitions on the P-31 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 P-31 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 P-31 donor electrons are in agreement with the prediction by de Sousa that they are limited by interface-defect induced field noise.