Carol Trager-Cowan , S. McArthur, P. G. Middleton, K. P. O'Donnell
Department of Physics and Applied Physics, University of Strathclyde
D. Zubia, S. D. Hersee
CHTM, University of New Mexico, Albuquerque
0).
A comparative study of these epilayers was undertaken using photoluminescence
(PL) spectroscopy, atomic force microscopy (AFM), scanning electron microscopy
(SEM), cathodoluminescence (CL) imaging, CL spectroscopy and Hall effect
measurements. Low temperature PL of the 0° and 4°
epilayers shows donor bound exciton (BE) emission between 3.47 and 3.48 eV and
a low level of yellow band emission. The peak intensities of both emission
bands are a factor of 2 higher for the 4° layer. In the
10° epilayer, the BE band is 3x stronger than in the 0°
epilayer but there is no discernible yellow band. However, a number of
additional bands appear at 3.459, 3.417, 3.362, 3.345, 3.309, and 3.285 eV.
These bands, some of which are acceptor related, may be attributed to the
presence of structural defects in this epilayer, pointing to an abrupt
degradation of its structural quality compared to the others. This degradation
is confirmed by AFM studies. On a 20 µm x 20 µm image the
0° and 4° epilayers exhibit smooth surface morphologies,
while the 10° epilayer shows a high density of hexagonal pits.
Finally, SEM images reveal the surface of the 10° epilayer to be
"streaked" and pitted. Low temperature CL images at 3.48 eV (bound
exciton region) show random spotty emission, while those at 3.28 eV and 3.41 eV
exhibit a streaky appearance similar to the SEM image. This suggests that
these luminescence bands are indeed associated with structural
defects.© 1998 The Materials Research Society