III-N ternary epi-layers grown on the GaN bulk crystals

The single crystals of GaN were grown at a high pressure of 10-20 kbar and a high temperature of 1500-1800 degreesC. The crystals have the form of hex agonal platelets of size up to 100mm(2) and dislocation density smaller tha n 10(3)cm(-2). These crystals were used as substrates for epitaxy of III-N compounds. Measurements indicate that the crystallographic structure of the substrates is reproduced in the epi-layers of the ternary compounds. AlGaN and InGaN, of compositions and thicknesses used in most of the nitride-bas ed devices. including a blue-laser structure. The very low dislocation dens ity in these layers and their structures is documented by X-ray diffraction , atomic force microscopy and high-resolution transmission electron microsc opy. The multiple quantum wells of InGaN/GaN have very sharp interfaces not disturbed by the presence of dislocations. (C) 2001 Elsevier Science B.V. All rights reserved.