Effect of low-energy nitrogen molecular-ion impingement during the epitaxial growth of GaAs on the photoluminescence spectra

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Abstract
Low-energy (∼100 eV) nitrogen molecular ions (N2+) were impinged during molecular beam epitaxial growth of GaAs at the substrate temperature of 550 °C. In the low-temperature (2 K) photoluminescence (PL) spectra, extremely sharp N-related emissions (Xi, i=1, 2, and 5) were observed in as-grown condition. These emissions were roughly two orders of magnitude stronger than those formed by the impingement of nitrogen atomic ions (N+). The results indicate that nitrogen (N) atoms are in situ substituted at As sites without inducing large structural damages and become quite efficient radiative recombination centers as isoelectronic impurities in GaAs. Further, to study the substitutional condition of N isoelectronic impurity, N isotope (15N) doped GaAs was grown by N152+ ion impingement. When N15 is doped, PL peak energy of X5 shifted towards higher energy side by 1.8 meV. The value is fairly close to the expected one of 1.9 meV when N15 replaces N14N. Together from energy separation between X2 emission (∼60 meV), origin of X5 was ascribed to the local vibrational mode of X2 emission.

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