Optical characterisation of GaN and related materials (original) (raw)
Related papers
Photoluminescence Excitation Studies of the Optical Transitions in GaN
MRS Proceedings, 1996
ABSTRACTWe present a detailed photoluminescence excitation study of the optical transitions in GaN. This technique is employed to distinguish between band-to-band excitation and exciton contribution to the formation of the free exciton, bound exciton, violet and yellow photoluminescence bands. We show the dominant role of the Fröhlich polar intraband scattering in the formation of the free exciton states. We demonstrate that bound exciton states in a large extent are created by the capture of the free excitons by shallow impurities as well as by phononassisted resonant excitation of the bound exciton states. The capture of the free carriers excited in the band continuum is a main excitation source for the violet and yellow bands. However, distinct A- and C-exciton resonances are detected in the excitation spectra of the violet and yellow emission bands.
Exciton-related photoluminescence in homoepitaxial GaN of Ga and N polarities
Applied Physics Letters, 2000
A photoluminescence ͑PL͒ study of GaN homoepitaxial layers grown by metal-organic chemical-vapor deposition demonstrates the high optical quality of N-face layers deposited on vicinal (0001 ) GaN substrates. In contrast to broad PL emission in exact (0001 ) layers, narrow-bound ͑0.9 meV͒ and free-͑A and B͒ excitonic transitions are observed. By following the PL spectra as a function of temperature and excitation power, the main optical transitions in the Ga-and the misoriented N-face layers are found to be the same. Observed differences are related to the distinct creation of donor and acceptor states in the samples of different polarities.
Photoluminescence and optical gain in highly excited GaN
Journal of Luminescence, 1997
A systematic study of the near-band-edge photoluminescence of epitaxially grown GaN as a function of excitation density has been carried out. While at low densities free and bound-exciton emission lines govern the spectrum, new luminescence bands are detected at densities above 1 MW/cm'. Gain measurements and temperature-dependent investigations indicate that nonlinear processes like biexciton annihilation, exciton-exciton-scattering and stimulated A-LO-emission are dominant at low temperatures, while exciton-free-carrier scattering occurs at temperatures above 200 K.
Solid State Communications, 1996
In this work we report results of photoluminescence (PL) and reflectivity meas~ements in the exciton region of GaN homoepit~ial layers grown by metalorganic chemical vapour deposition on GaN substrates. At low temperature (4.2K), very narrow (FWHM = i.OmeV) PL lines related to excitons bound to neutral acceptor (3.4666eV) and neutral donor (3.4719eV) were observed. The energies of gee excitons fi-om re~e~ti~~ and PL measurements were found to be: E,= 3.4780eV, Ea= 3.4835eV and EC= 3.502eV.
Applied Physics Letters, 1995
Neutral-donor-bound exciton recombination (I2) dynamics have been studied by photoluminescence in an unintentionally doped n-type GaN epitaxial layer grown by metalorganic chemical vapor deposition. The luminescence emission line shape, peak position, and intensity as functions of temperature have been measured. In particular, time-resolved emission spectroscopy has been employed to study the dynamic processes of the bound exciton recombination, from which the temperature and the emission energy dependencies of the recombination lifetime of this transition have been obtained.
Optical characterization of AlN/GaN heterostructures
2003
AlN/GaN/sapphire heterostructures with AlN gate film thickness of 3-35 nm are characterized using photoreflectivity ͑PR͒ and photoluminescence ͑PL͒ spectroscopy. Under a critical AlN film thickness, the luminescence from the GaN channel layer near the interface proves to be excitonic. No luminescence related to the recombination of the two-dimensional electron gas ͑2DEG͒ is observed, in spite of high 2DEG parameters indicated by Hall-effect measurements. The increase of the AlN gate film thickness beyond a critical value leads to a sharp decrease in exciton resonance in PR and PL spectra as well as to the emergence of a PL band in the 3.40-3.45 eV spectral range. These findings are explained taking into account the formation of defects in the GaN channel layer as a result of strain-induced AlN film cracking. A model of electronic transitions responsible for the emission band involved is proposed.