High-quality GaN films obtained by air-bridged lateral epitaxial growth

High-quality GaN films with low dislocation density and low wing tilt of c- axis orientation have been successfully obtained by a promising technique o f selected area growth, namely air-bridged lateral epitaxial growth (ABLEG) . A GaN film was grown from the exposed (0001) top facet of the ridged GaN seed structures, whose side walls and etched bottoms were covered with sili con nitride mask, using low-pressure metalorganic vapor-phase epitaxy. The ridge-stripe structures of the GaN seed were constructed in the <1 (1) over bar 00 > (GaN) direction. At the optimum growth temperature of 950 degrees C, only the {11 (2) over bar0} and {0001} facets were obtained. Continuing the growth led to fabricating the air-bridged structure, where the coalesce nce of the wing region occurred. From the transmission electron microscopy study, it was found that most of the vertical dislocations along the c-axis were confined to the seed region, while the horizontal dislocations were n ewly generated in the vicinity of coalescence boundary. The densities of th e vertical dislocations were about 9 x 10(8) cm(-2) in the seed region, whi le below 1 x 10(6) cm(-2) in other regions. The densities of the horizontal dislocations were about 1 x 10(6) cm(-2) in the wing region and 4 x 10(7) cm(-2) in the vicinity of the coalescence boundary, respectively. The X-ray diffraction (XRD) measurements revealed that the tilt angle of c-axis rela tive to underlying seed GaN was about 297 arcsec (0.083 degrees), and the f ull-width at half-maximum of the XRD curve for the wing region was 138 arcs ec, indicating that the wing region has high uniformity of c-axis orientati on. Both of the wing and the coalescence boundary region exhibited atomical ly smooth surfaces with stepped terraces, whose root mean square roughness was found to be 0.089 nm by atomic force microscopy measurements. (C) 2000 Elsevier Science B.V. All rights reserved.