Effect of Al mole fraction on structural and electrical properties of Al_xGa_(1-x) N/GaN heterostructures grown by plasma-assisted molecular beam epitaxy

摘要

The effect of Al mole fractions on the structural and electrical properties of Al_xGa_(1-x)N/GaN thin films grown by plasma-assisted molecular beam epitaxy (PA-MBE) on Si (111) substrates has been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and current-voltage (I-V) measurements. X-ray results revealed that the AlGaN/GaN/AIN was epitaxially grown on Si substrate. By applying Vegard's law, the Al mole fractions of Al_xGa_(1-x)N samples were found to be 0.11, 0.24,0.30 and 0.43, respectively. The structural and morphology results indicated that there is a relatively larger tensile strain for the sample with the smallest Al mole fraction; while a smaller compressive strain and larger grain size appear with Al mole fraction equal to 0.30. The strain gets relaxed with the highest Al mole fraction sample. Finally, the linear relationship between the barrier height and Al mole fraction was obtained.