Exciton dynamics in thick GaN MOVPE epilayers deposited on sapphire.
J. Allègre, P. Lefebvre, J. Camassel
Groupe d'Etude des Semiconducteurs, GES-CNRS
B. Beaumont, Pierre Gibart
Centre de Recherche sur l'Hetero-Epitaxie et ses Applications, CRHEA-CNRS
This article was received on June 10, 1997 and
accepted on September 15, 1997. Abstract
Time-resolved photoluminescence spectra have been recorded on
three GaN epitaxial layers of thickness 2.5 µm, 7 µm and 16 µm, at
various temperatures ranging from 8K to 300K. The layers were deposited by
MOVPE on (0001) sapphire substrates with standard AlN buffer layers. To achieve
good homogeneities, the growth was in-situ monitored by laser reflectometry.
All GaN layers showed sharp excitonic peaks in cw PL and three excitonic
contributions were seen by reflectivity. The recombination dynamics of excitons
depends strongly upon the layer thickness. For the thinnest layer, exponential
decays with 
~ 35 ps have been measured for both XA and
XB free excitons. For the thickest layer, the decay becomes
biexponential with 1 ~ 80 ps and 2 ~ 250 ps.
These values are preserved up to room temperature. By solving coupled rate
equations in a four-level model, this evolution is interpreted in terms of the
reduction of density of both shallow impurities and deep traps, versus layer
thickness, roughly following a L-1 law.
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Cite this article as: MRS Internet J. Nitride Semicond. Res. 2, 32(1997).
last updated October 17, 1997 11:00:44 AM.© 1997 The Materials Research Society
