Optical characterization of low-energy nitrogen-ion doped GaAs

Optical characterization of nitrogen (N)-doped GaAs was performed by low-temperature photoluminescence (PL) measurements. N doping in GaAs was successfully made by irradiating low-energy (100 eV) N⁺ ion beam during the growth of GaAs using the combined ion beam and molecular beam epitaxy (CIBMBE) system. For the sample with N⁺ ion beam current density (I_N) of 3 nA/cm², which correspond to N concentration ([N]) of ∼ 5 × 10¹⁷ cm^-3, two sharp PL emissions were observed at 1.508 eV (X₁) and 1.495 eV (X₂). For the sample with I_N of 75 nA/cm² ([N]≈ 1 × 10¹⁹ cm^-3), several novel PL emissions tentatively labeled by Y_j (j = 1, ..., 8) were observed in the energy range of 1.491-1.449 eV by furnace annealing at 750°C for 20 min. Photoluminescence excitation measurements indicated that X₁ is correlated with the PL emission at 1.514 eV. Since the energy separation between individual Y_j (j = 1, ..., 8) and X₂ is almost linear to r^-3 _k, where r_k is the distance between nitrogen-nitrogen (NN) pairs, we ascribed X₂ and Y_j as the radiative transition of excitons bound to isolated N and that to N-N pairs, respectively.