Defect reduction in (112¯) a-plane GaN by two-stage epitaxial lateral overgrowth

Abstract

In the epitaxial lateral overgrowth (ELO) of (1120) a-plane GaN, the uneven growth rates of two opposing wings, Ga-and N-wings, makes the coalescence of two neighboring wings more difficult than that in c-plane GaN. We report a two-stage growth method to get uniformly coalesced epitaxial lateral overgrown a-plane GaN using metalorganic chemical vapor deposition (MOCVD) by employing relatively lower growth temperature in the first step followed by enhanced lateral growth in the second. Using this method, the height differences between Ga-polar and N-polar wings at the coalescence front could be reduced, thereby making the coalescence of two wings much easier. Transmission electron microscopy (TEM) showed that the threading dislocation density in the wing areas was 1.0×10 8 cm -2 , more than two orders of magnitude lower than that in the window areas (4.2×10 10 cm -2 ). However, high density of basal stacking faults of 1.2×10 4 cm -1 was still observed in the wing areas as compared to c-plane GaN. Atomic force microscopy and photoluminescence

Exciton localization on basal stacking faults in a-plane epitaxial lateral overgrown GaN grown by hydride vapor phase epitaxy

“…Rarely observed away from the substrate in c-plane GaN, BSFs are found in a-plane samples with densities as high as 10 5 cm −1 , as already reported by other groups. 9 Stampfl and Van de Walle 10 identified four different types of BSFs. The one that we observe here is the I 1 type, which consists of one violation of the stacking sequence: if the fault starts on a Bb layer, the stacking sequence is then ...AaBbAaBbCcBbCcBbAaBb.…”

“…Several groups have recently reported on the fabrication of a-plane GaN templates using the epitaxial lateral overgrowth ͑ELO͒ technique with improved surface morphology and material quality in the two types of so-called "wing" regions 4,5 that grow along the +c ͑Ga-face͒ and −c ͑N-face͒ directions. We have used a similar approach.…”

Defect reduction in overgrown semi-polar (11-22) GaN on a regularly arrayed micro-rod array template

“…The ratio of this area to the area of integrated line segment AE along the m-direction can be treated as a dislocation remaining ratio. For simplicity, any decrease in dislocation density due to the lateral overgrowth along the a-direction and a very small number of extra dislocations generated during the coalescence processes 11,25 are not taken into account. Figure 4(b) shows our simulation result, describing the relationship between the dislocation remaining ratio and micro-rod diameter & spacing between micro-rods, where the height of micro-rods is set as 0.4 and 1.4 µm as two examples, respectively.…”

Intrinsic dynamics of weakly and strongly confined excitons in nonpolar nitride-based heterostructures

“…2 However, lattice-mismatched substrates such as sapphire or LiAlO 2 are generally used to grow nonpolar GaN, inducing strain in the heteroepitaxial layers. 3,4 Strain relaxation through the generation of dislocations or basal stacking faults leads to a drastic reduction of exciton lifetime: even when sophisticated processing techniques such as epitaxial lateral overgrowth are used, exciton dynamics is dominated by the capture on these extended defects. [5][6][7] In the present work, we overcome such difficulties by using molecular beam epitaxy (MBE) to grow a nonpolar nitride-based heterostructure on the a-facet of a GaN single crystal elaborated by the combination of a high-pressure solution method and hydride vapor phase epitaxy (HVPE).…”