PREPARATION OF ALXGA1-XN/GAN HETEROSTRUCTURE BY MOVPE

The AlxGa1-xN/GaN heterostructure (HS) is prepared by metalorganic vapor phase epitaxy (MOVPE) at atmospheric pressure on sapphire substrate. The surface morphology of the AlxGa1-xN/GaN HS is investigated. When the AlxGa1-xN layer is thinner than a certain thickness (hc), the surface is smooth and has no cracks. While when the layer is thicker than hc, many cracks and V-shaped grooves appear in the AlxGa1-xN and GaN layers, and their densities increase with increasing x. The mechanism of the cracking is the relaxation of the strain energy due to the lattice misfit between AlxGa1-xN and GaN during the growth, but not due to the difference in thermal expansion coefficient between AlxGa1-xN and GaN during the cooling after the growth. For the preparation of the AlxGa1-xN/GaN HS with a smooth surface free from cracks, it is important to control the thickness and the composition of the AlxGa1-xN layer. © 1990.