Twin photoluminescence peaks from single isoelectronic traps in nitrogen δ-doped GaAs

We report on twin emission peaks observed from single isoelectronic traps formed by nitrogen pairs in nitrogen δ-doped GaAs by high-energy resolution micro-photoluminescence (PL) spectroscopy. The twin PL peaks show almost the same intensity with narrow linewidths of 20−50 μeV, which are considerably smaller than that ever reported for isoelectronic traps in GaAs:N. The higher and lower energy luminescence transitions were linearly polarized in the [1 1¯ 0] and [1 1 0] directions, respectively, indicating that the two exciton states have completely orthogonal relations with each other. The fact that any pair of the twin PL peaks has the same polarization properties suggests that the splitting is due to the anisotropy between [1 1¯ 0] and [1 1 0] directions in the host crystal and is possibly explained by the strain anisotropy in the sample.