Isoelectronic nitrogen δ-doping in GaP and single-photon emission from individual nitrogen pairs

Nitrogen (N) δ-doping in GaP was studied using low-pressure metalorganic chemical vapor deposition at 650 °C. Secondary ion mass spectroscopy measurements revealed that the profile of atomic N concentrations is abrupt and symmetrical, indicating a good-quality δ-doping. For the δ-doped sample of a dilute N sheet density, spatially dependent emission spectra from N-related isoelectronic traps were observed at 30 K with micro-photoluminescence (μ-PL). Besides the well-known NNi pairs, as well as the so-called A line, a new peak was observed at 2.2847 eV. We successfully mapped the spatial distribution of NN4 pairs by using 0th order diffraction of a spectrometer with a narrow-band pass filter. By applying this technique to several samples with different N sheet densities, it was found that the densities of NNi and the new peak have square and cubic dependence on the sheet density of N atoms, respectively. After identifying a single NN4 pair using the μ-PL, strong photon antibunching under continuous optical pumping was demonstrated, which is good evidence for clear single-photon emission from an individual N–N pair.