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

Abstract

High-quality GaN films with low dislocation density and low wing tilt of c-axis orientation have been successfully obtained by a promising technique of selected area growth, namely air-bridged lateral epitaxial growth (ABLEG). A GaN film was grown from the exposed (0 0 0 1) top facet of the ridged GaN seed structures, whose side walls and etched bottoms were covered with silicon nitride mask, using low-pressure metalorganic vapor-phase epitaxy. The ridge-stripe structures of the GaN seed were constructed in the 1 1 ̄ 00 GaN direction. At the optimum growth temperature of 950°C, only the 1 1 2 ̄ 0 and {0 0 0 1} facets were obtained. Continuing the growth led to fabricating the air-bridged structure, where the coalescence 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 newly generated in the vicinity of coalescence boundary. The densities of the vertical dislocations were about 9×10 8 cm −2 in the seed region, while below 1×10 6 cm −2 in other regions. The densities of the horizontal dislocations were about 1×10 6 cm −2 in the wing region and 4×10 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 relative to underlying seed GaN was about 297 arcsec (0.083°), and the full-width at half-maximum of the XRD curve for the wing region was 138 arcsec, indicating that the wing region has high uniformity of c-axis orientation. Both of the wing and the coalescence boundary region exhibited atomically smooth surfaces with stepped terraces, whose root mean square roughness was found to be 0.089 nm by atomic force microscopy measurements.