Determination of Wurtzite GaN Lattice Polarity Based on Surface Reconstruction

We identify two categories of reconstructions occurring on wurtzite GaN surfaces, the first associated with the N-face, (000 ), and the second associated with the Ga-face, (0001). Not only do these two categories of reconstructions have completely different symmetries, but they also have different temperature dependence. It is thus demonstrated that surface reconstructions can be used to identify lattice polarity. Confirmation of the polarity assignment is provided by polarity-selective wet chemical etching of these surfaces. The potential applications for blue light emitting devices continue to drive research efforts to understand the growth of GaN. In the fabrication of most nitride-based devices, epitaxial growth occurs on the c-plane of wurtzite GaN. A key characteristic of wurtzite GaN is its polarity. No symmetry operation of the crystal relates the [0001] to the [000 ] direction, and so the (0001) and (000 ) surfaces are inequivalent. The former surface is known as the Ga-face, and the latter as the N-face. While the atomistic details of surface structure are known to govern growth kinetics, little has been understood, until recently, about the surface structures of wurtzite GaN. Remarkably, a few groups have reported the inability to observe any surface reconstructions at all on wurtzite GaN other than a 1×1.[1,2] At the same time, a number of other groups have reported a variety of reflection high energy electron diffraction (RHEED) patterns, including 1×1, 2×1, 2×2, 2×3, 3×2, 3×3, 4×4, and 5×5.[3-9] However, the polarities of the surfaces which gave these diffraction patterns were unknown. Recently, we have identified the surface reconstructions which belong to the N-face of wurtzite GaN, which include 1×1, 3×3, 6×6, and c(6×12).[10] In this paper, we summarize those findings and identify, in addition, the surface reconstructions which belong to the Ga-face, show1