Abstract
We study the growth of AlxGa1−x Nepilayers on (0001) sapphire by low-pressure MOCVD, using alow-temperature AlN buffer. By varying the input flow rates oftrimethylgallium (TMGa), we obtain crack-free AlGaN films in the wholerange of composition. A linear relationship between gas and solid Alcontent is observed. The structural properties of the layers (x = 0−1)are investigated by x-ray diffraction, atomic force microscopy (AFM)and scanning electron microscopy (SEM). It is found that atwo-direction growth appears along the c-axis and the (101̄1) directionsfor x⩾0.45. From the results of Raman spectroscopy, we suggest thatthe compressive stain and the lack of mobility of Al adatoms can inducethe formation of (101̄1) grains.
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