(Color online) Schematic of nanocomposite synthesis and layer transfer. (a) An ion-implanted GaAs substrate is bonded to a new substrate using a spin-on glass layer. (b) Following thermal annealing, GaN nanocrystals nucleate in the GaAs matrix, forming a GaAs:N nanocomposite layer. Simultaneously, nitrogen gas bubbles lead to interfacial cracking between the GaAs:N nanocomposite layer and GaAs substrate, inducing separation from the GaAs substrate. In principle, the damaged layer of the “parent” GaAs substrate may be polished off and the parent substrate recycled for further processing.
(Color online) Improved transfer quality of GaAs:N nanocomposite layers with various bonding conditions. SEM and AFM images of GaAs:N layers transferred to alumina with bonding layers consisting of (a) and (b) ∼1 μm “thick” PMSSQ SOG, (c) and (d) ∼200 nm “thin” PMSSQ SOG, and (e) and (f) ∼200 nm “thin” BTSE-MTMS SOG. The SEM image of the surface of the transferred layer bonded with thick PMSSQ in (a) reveals surface “channel” cracks. As shown in the AFM image and corresponding line-cut in (b), these cracks penetrate through the ∼200 nm thick transferred layer to the substrate. A comparison of the SEM images for the “thick” and “thin” PMSSQ SOG layers in (a) and (c) reveals that the roughness of the transferred layer is reduced by decreasing the thickness of the PMSSQ SOG layer. However, the AFM image and corresponding line-cut for the “thin” PMSSQ SOG in (d) reveals pit defects (highlighted by dashed circles) with depths approximately equal to the transferred layer thickness, suggesting that localized blister formation occurs instead of layer transfer, possibly due to the formation and spalling of blisters in localized areas with insufficient bonding. For the thermally-matched BTSE-MTMS SOG, these defects are apparently eliminated, as shown by the SEM and AFM images in (e) and (f).
Nanostructure formation in transferred layers. (a) Bright-field, and (b) dark-field cross-sectional TEM images of GaAs:N layers transferred to an Al2O3 substrate. (c) Bright-field, and (d) dark-field cross-sectional TEM images of GaAs:N layers transferred to an AlN substrate. In both (b) and (d), corresponding SAED patterns are shown as insets. The SAED patterns of the transferred GaAs:N layers indicate the presence of both zincblende (ZB) GaAs and ZB GaN crystallites. In the dark-field TEM images in (b) and (d), dashed lines indicate smooth interfaces between the GaAs:N nanocrystal and SOG bonding layers. Furthermore, nanometer-size bright features in the GaAs:N layers, indicated by arrows, confirm the formation of nanocrystallites.
High-resolution TEM images of transferred nanocomposite layers. Examples of nanometer-sized GaN crystallites are circled for layers transferred to (a) Al2O3, and (b) AlN substrates.
Comparison of the interplanar distances measured by selected area electron diffraction of the GaAs:N nanostructured layers with the powder diffraction standards for zincblende (ZB) GaN and GaAs.
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