Materials Research Society Symposium Proceedings 468, 23 (1997).
Below is the abstract submitted to the meeting, not the abstract of the published paper:
AlGaN is an important material for the realization of nitride heterostructures, involved in most device designs. We have studied the growth of this alloy using low pressure MOVPE (76 Torr), using triethyl gallium (TEGa), trimethyl-aluminium (TMAl) and ammonia (NH3) as precursors. First the solid-gas aluminium segregation was studied in order to calibrate the incorporation of Al in the solid phase. We found that aluminium is more readily incorporated than gallium in the solid, leading to an apparent Al segregation coefficient greater than unity. A simple kinetic model is used to fit the experimental data and is discussed versus structural arguments (bond lengths in AlN and GaN, atomic and ionic radii, ...). Scanning electron microscopy has been used to investigate the morphology of the samples through the whole range of Al content (x = 0 to 0.9), and we observe a clear evolution of the surface features versus aluminium concentration: at low Al contents, small (below 1 um) hexagonal holes are observed while at high Al, acicular features are observed, with a sudden transition between those morphologies around x = 0.5. This is discussed in terms of growth kinetics. Finally, the samples were studied by low temperature (2K) reflectivity and we will report the evolution of the optical quality of samples (x < 0.4) versus growth parameters, as evaluated from the broadening of the observed excitonic transitions in the 2K reflectivity.
This paper is part of Gallium Nitride and Related Materials II
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