Effect of rapid thermal annealing: red and blue shift in photoluminescence of GaNAs grown by RF plasma-assisted molecula
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Effect of rapid thermal annealing: red and blue shift in photoluminescence of GaNAs grown by RF plasma-assisted molecular beam epitaxy W.K. Loke, S. F. Yoon, T. K. Ng, S. Z. Wang and W. J. Fan Nanyang Technological University, School of Electrical and Electronic Engineering, Block S1, Nanyang Avenue, Singapore 639798, Republic of Singapore ABSTRACT Rapid thermal annealing (RTA) of 1000Å GaNAs films grown on (100) oriented GaAs substrate by radio frequency (RF) plasma assisted solid-source molecular beam epitaxy was studied by low-temperature photoluminescence (PL) and high-resolution x-ray diffraction (HRXRD). Samples with nitrogen content of 1.3 and 2.2% have shown an overall blueshift in energy of 67.7meV and an intermediate redshift of 42.2meV in the PL spectra when subjected to RTA at 525-850oC for 10min. It is also shown that the sample, which is annealed at temperature range of 700-750oC, has the highest photoluminescence efficiency (1.7-2.1 times increase in integrated PL intensity as compared to the as-grown sample). Reciprocal space mapping of the as-grown GaNAs samples obtained by using triple-crystal HRXRD shows the presence of interstitially incorporated of N atoms with no lattice relaxation in the direction parallel to the growth surface. These results have significant implication on the growth and post-growth treatment of nitride compound semiconductor materials for high performance optoelectronics devices. INTRODUCTION Group III-N-As is a promising material for 1.3 and 1.55µm telecommunication optoelectronic devices grown on GaAs substrate. Hence, epitaxial growth of the nitride compound has been studied extensively. It is known that the luminescence efficiency of these alloys can be greatly improved by annealing at temperature higher than the growth temperature [1]. The same has been reported for quantum well structures of GaNAs/GaAs [2]. However, along with large improvement in the PL efficiency, a significant blueshift (9-50meV) of the maximum PL intensity position was also observed which seemed independent of the N composition. This blueshift effect in the PL peak energy has been attributed mainly to two possible reasons; (i) nitrogen out-diffusion from bulk GaNAs [3], and (ii) interdiffusion of N-As atoms near the interface of GaNAs/GaAs [4,5]. However, the results from our experiments suggest the presence of a different mechanism of diffusion. This is shown by an intermediate redshift in the PL peak energy in annealing temperature range lower than the optimum temperature. Furthermore, such changes were not accompanied by a shift towards higher Bragg angle for the GaNAs peak in HRXRD, a result different from others [6,7].
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EXPERIMENTAL DETAILS All our samples were grown by solid-source molecular beam epitaxy (SSMBE) with nominal structures of 200Å GaAs/1000Å GaNAs/3000Å GaAs buffer layer on semi-insulating GaAs (100) substrate using elemental sources of gallium (7N), arsenic (6N) and a nitrogen radiofrequency (RF) plasma source. Prior to growth of GaNAs, oxide desorption was carried out
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