Electronic structure of the substitutional nitrogenNN1pair in GaP from photoluminescence excitation and Zeeman spectroscopy

Novel photoluminescence (PL) data are presented for the nearest-neighbor substitutional ${\mathrm{NN}}_1$ (${\mathrm{N}}_{\mathrm{P}}$-${\mathrm{N}}_{\mathrm{P}}$) pair defect in GaP, with a bound exciton (BE) at 2.185 eV at 2 K. The zero-field electronic line spectrum of this BE is accurately determined via photoluminescence excitation (PLE) spectra, which give the relative oscillator strengths of the six PL lines resolved. In addition Zeeman data are obtained for magnetic fields up to 7 T, including the full angular dependence. An explicit expression is derived for the evaluation of the zero-field splitting of the BE substates, in terms of the electron-hole (e-h) exchange parameter a and the crystal-field parameters D and E. Computer-simulated relative oscillator strengths obtained with a simple basis set of spinlike electrons and J=(3/2 holes show a good agreement with the observed relative intensities of the electronic BE lines in PLE spectra. The Zeeman data were analyzed with a complete Hamiltonian including the zero-field perturbations. The evaluated parameter values are a=0.585 meV, D=0.20 meV, E=0.095 meV, $g_e$=1.85, K=1.21, and L=-0.05, with conventional notations. The zero-field parameters a, D, and E in particular differ markedly from earlier less accurate data, while the magnetic parameters $g_e$, K, and L are in agreement with earlier estimates, although more accurate. The data confirm a $C_{2v}$ symmetry of the defect, as was previously deduced from uniaxial stress perturbations.