Structural characterization and strain relaxation in porous GaN layers

Abstract

Surface and subsurface structures of porous GaN prepared by anodizing epitaxial GaN layers grown on SiC substrates are investigated by atomic-force microscopy. Comparison of the images of the porous GaN surfaces with those taken on planes cleft perpendicular to the surface shows that the pores are formed along the boundaries of columnar structures of the original GaN films. X-ray investigations show that the porous GaN has less residual stresses than the initial GaN epitaxial layers. Use of porous GaN as a buffer layer for growth of low-stress GaN is proposed.

Growth of GaN on Porous SiC by Molecular Beam Epitaxy

“…It was found that the pores extended vertically down into the layer, i.e. following the columnar nature of the film [20]. By removing material from around the columns, the material inside the columns can elastically relax (so long as the depth of the etched material is comparable to the width of the column).…”

“…It was found in previous work that use of porous substrates can lead to significant strain relaxation in the film, at least in certain cases [20] [21].…”

“…This conclusion is, perhaps, not surprising when we carefully consider the geometry of the situation. The prior work which did observe a strain reduction was for GaN growth on porous GaN, employing a GaN buffer layer that was then etched to make it porous [20] [21]. It was found that the pores extended vertically down into the layer, i.e.…”

Combined MOCVD and MBE growth of GaN on porous SiC

“…Earlier studies have shown improved GaN film quality on porous SiC [2][3][4]. It was recently shown that the GaN grown by molecular beam epitaxy (MBE) on porous SiC is considerably more strain relaxed than the GaN grown on nonporous SiC [7].…”

“…Porous SiC has attracted considerable interest in the recent years as an attractive substrate for epitaxy of GaN and SiC [1][2][3][4][5][6]. Earlier studies have shown improved GaN film quality on porous SiC [2][3][4].…”