Hyperfine structure and nuclear hyperpolarization observed in the bound exciton luminescence of Bi donors in natural Si

TL;DR

This paper investigates the hyperfine structure and nuclear hyperpolarization in Bi donor bound excitons in silicon, revealing strong hyperpolarization effects and introducing a new model to explain these phenomena.

Contribution

The study provides the first detailed observation of hyperfine interactions and hyperpolarization in Bi donors in silicon, along with a novel model explaining the hyperpolarization mechanism.

Findings

Resolved hyperfine splitting in photoluminescence spectrum.

Observation of nuclear hyperpolarization with opposite sign to equilibrium.

Proposed a new model predicting rapid hyperpolarization dynamics.

Abstract

As the deepest group V donor in Si, Bi has by far the largest hyperfine interaction, and also a large I=9/2 nuclear spin. At zero field this splits the donor ground state into states having total spin 5 and 4, which are fully resolved in the photoluminescence spectrum of Bi donor bound excitons. Under a magnetic field, the 60 expected allowed transitions cannot be individually resolved, but the effects of the nuclear spin distribution, -9/2 <= I_z <= 9/2, are clearly observed. A strong hyperpolarization of the nuclear spin, with sign opposite to the expected equilibrium polarization, is observed to result from the nonresonant optical excitation. This is very similar to the recently reported optical hyperpolarization of P donors observed by EPR at higher magnetic fields. We introduce a new model to explain this effect, and predict that it may be very fast.