Cathodoluminescence, photoluminescence and
optical absorbance spectroscopy of aluminum gallium nitride
(AIxGa1-xN)
filmsL.H. Robins
Lowney
(
Institute of Standards and Technology,
Hopkins University)
Aluminum
gallium nitride
(AlxGa1-xN) films, grown
by metal-organic chemical vapor deposition on sapphire, were
characterized by low-temperature cathodoluminescence (CL) and
photoluminescence (PL), and room-temperature optical absorbance. The
aluminum fractions are estimated to range from x = 0 to x = 0.444. Most
films were silicon-doped. The absorption spectra have an Urbach
(exponential) form below the bandgap. The width of the Urbach edge,
EU, increases with Al fraction, x, as
EU = (0.045 + 0.104x)eV. The luminescence (CL or
PL) spectra show a relatively narrow band-edge peak and a broad deep-level
peak. The full-widths at half-maximum of the band-edge CL peaks (measured
at T = 15 K) are remarkably similar to the Urbach absorption widths,
EU (measured at T = 300 K). PL spectra were
obtained from the top surfaces and the film-substrate interfaces of
several films. The interface PL spectra of some films show an extra peak
0.15 eV to 0.45 eV below the bandgap, which is ascribed to structural
defects or impurity phases localized near the interface. The energy of
the band-edge luminescence peak shifts with excitation mode (CL,
top-surface PL, or interface PL). This effect is attributed to the
variation of the excitation depth, between the top surface and
film-substrate interface, with excitation mode, together with the depth
varia-tion of film properties such as residual stress or aluminum
fraction.
Order No.:
JA809-021 © 1998 MRS
Go to September 1998 Table of Contents
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