Optical and structural study of GaN nanowires grown by catalyst-free molecular beam epitaxy. II. Sub-band-gap luminescence and electron irradiation effects
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)
GaN nanowires with diameters of 50-250 nm, grown by catalyst-free molecular beam epitaxy, were characterized by photoluminescence (PL) and cathodoluminescence (CL) spectroscopy at temperatures from 3 to 297 K. Both as-grown samples and dispersions of the nanowires onto other substrates were examined. The properties of the near-band-edge PL and CL spectra were discussed in Part I of this study by [Robins et al. [L. H. Robins, K. A. Bertness, J. M. Barker, N. A. Sanford, and J. B. Schlager, J. Appl. Phys. 101,113505 (2007)]. Spectral features below the band gap, and the effect of extended electron irradiation on the CL, are discussed in Part II. The observed sub-band-gap PL and CL peaks are identified as phonon replicas of the free-exciton transitions, or excitons bound to structural defects or surface states. The defect-related peaks in the nanowires are correlated with luminescence lines previously reported in GaN films, denoted the Y lines [M. A. Reshchikov and H. Morkoc, J. Appl. Phys. 97, 061301 (2005)]. The CL was partially quenched by electron beam irradiation for an extended time; the quenching was stronger for the free and shallow-donor-bound exciton peaks than for the defect-related peaks. The quenching appeared to saturate at high irradiation dose (with final intensity {approx_equal}30% of initial intensity) and was reversible on thermal cycling to room temperature. The electron irradiation-induced quenching of the CL is ascribed to charge injection and trapping phenomena.
- OSTI ID:
- 20979411
- Journal Information:
- Journal of Applied Physics, Vol. 101, Issue 11; Other Information: DOI: 10.1063/1.2736266; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ABSORPTION SPECTRA
CATHODOLUMINESCENCE
CRYSTAL DEFECTS
CRYSTAL GROWTH
ELECTRON BEAMS
ENERGY GAP
EXCITONS
GALLIUM NITRIDES
IRRADIATION
MOLECULAR BEAM EPITAXY
PHONONS
PHOTOLUMINESCENCE
QUANTUM WIRES
QUENCHING
RADIATION DOSES
SEMICONDUCTOR MATERIALS
TEMPERATURE RANGE 0273-0400 K
THERMAL CYCLING
THIN FILMS