The defect character of GaN growth on r-plane sapphire

Abstract

We study the influence of the heteroepitaxial interface on the defect content of nonpolar a-plane GaN grown on r-plane sapphire, using transmission electron microscopy techniques and the topological theory of interfacial defects. The structural mismatch is accommodated in different ways along distinct in-plane directions. For the misfit along the [0001] direction of GaN, the I1 basal stacking faults constitute the principal relaxation mechanism, through their delimiting partial dislocations. The misfit along [11¯00] is relaxed by misfit dislocations that have out-of-plane Burgers vectors causing rotational misorientations of the epilayer about [0001]. These misorientations lead to the introduction of low-angle tilt grain boundaries which are defect sources through their associated primary lattice dislocations. Furthermore, semipolar nanocrystals can nucleate on sapphire p-plane nanofacets, causing the introduction of threading dislocations (TDs) and stacking faults, when these nanocrystals are overgrown by the nonpolar epilayer. The semipolar nanocrystals bear a high-symmetry 90° [1¯21¯0] orientation relative to the nonpolar epilayer. The interfacial dislocations at the nonpolar/semipolar boundaries have suitable Burgers vectors to become TDs. These grain boundaries also promote the introduction of stacking faults and pockets of cubic GaN. The coexistence of semipolar orientation variants leads to twin boundaries and associated dislocations.

HVPE growth of self-aligned GaN nanorods on c-plane, a-plane, r-plane, and m-plane sapphire wafers

“…The tilt angle as reported by many other groups is 58.9° [17,18]. The knowledge of the sap- Photoluminescence spectra of [11][12][13][14][15][16][17][18][19][20][21][22] inclined intertwined GaN nanorods on m-plane sapphire. The left-hand side shows the schematic variation in the incidence area, when the specimen is rotated through 0 to 360°in steps of 90°.…”

“…This can reduce the mismatch between the a-plane GaN epilayer and the r-plane sapphire substrates due to the misfit dislocations. Similar to the case of Nitridation in c- plane sapphire, here also, a parasitic semipolar (103) nanocrystals are formed, which is really a side effect [15,16]. The epitaxial relationship is given as 1 120 ½ nÀGaN k 1 102 ½ Sap and 1 100 ½ GaN k 1 120 ½ Sap .…”

Morphology and origin of V-defects in semipolar (11–22) InGaN

“…The interfacial nanocrystals consisted of nonpolar m-plane AlN, as described in detail elsewhere [20]. It has been shown for the case of a-plane GaN that such parasitic interfacial nanocrystals are sources of TDs [21]. It is noted that in cases where pits are not shown clearly to be connected to a TD, this could be due to the apex of the pit not being included in the TEM lamella.…”

“…The basal plane is the primary slip plane of the wurtzite structure and the shear stress is provided by the misfit since the basal plane is inclined relative to the growth direction. In addition to introduction of lattice dislocations by the Mathhews-Blakesley mechanism [23], they are further promoted by the misoriented nanocrystals at the heteroepitaxial interface with sapphire [21]. In addition to the lattice TDs, much larger is the density of partial dislocations that also reside on the basal plane since the SFs provide a mechanism of misfit relaxation [21,24,25].…”

“…In addition to introduction of lattice dislocations by the Mathhews-Blakesley mechanism [23], they are further promoted by the misoriented nanocrystals at the heteroepitaxial interface with sapphire [21]. In addition to the lattice TDs, much larger is the density of partial dislocations that also reside on the basal plane since the SFs provide a mechanism of misfit relaxation [21,24,25]. Lattice and partial TDs with c-type Burgers vector components arise as threading arms due to the relaxation of the misfit along the in-plane projection of the [0001] direction [24].…”