Controlling facets and defects of InP nanostructures in confined epitaxial lateral overgrowth

The selective area growth technique, confined epitaxial lateral overgrowth (CELO), enables the growth of lateral III-V heterojunctions integrated on mismatched substrates. In CELO, effective control of facet shapes, as well as defect-free growths are essential to fabricating high-quality nanostructures with custom geometries. Here, the effects of growth temperature, V/III ratio, template alignments, and substrate orientations on the observed facets and defect densities in CELO grown InP and related materials on InP substrates are investigated. The nanostructure facets and defects are determined using a combination of plan-view and cross-sectional transmission electron microscopy. For homoepitaxial CELO growth on InP (100) substrates, growth temperatures below $575{}^{\circ }\mathrm{C}$, and high V/III ratios of 450 aid in increasing the surface areas of the {111}B facets, while reducing defect densities. Further, by changing template alignments, the effective areas of overgrowth can be tuned, and defects can be lowered, with templates aligned along $\left[0\overline{1}0\right]$ yielding the largest defect-free areas. By aligning templates in the $\left[\overline{1}10\right]$ orientation on a (110) InP substrate, near defect-free overgrowth with perfectly flat perpendicular single ($1\overline{1}$ 0) facets can be achieved. This is an essential feature to enable the growth of lateral III-V heterojunctions, as is demonstrated by growing InP/InGaAs CELO heterojunctions with {110} facets.

Figure 1

(a) Schematic of CELO template before growth (a.i) and after III-V overgrowth (a.ii) (b), (c), respectively, show top-down scanning electron microscopy images of a CELO template before growth and after InP overgrowth. (d) High-angle annular dark field (HAADF) STEM of a plan-view lamella containing CELO structures post-InP growth. (e) Plan-view bright field STEM image of a CELO template with grown InP inside it. The light and dark contrast corresponds to regions with and without defects. (f) Cross-section HAADF STEM from the plan-view sample (e) along the red dashed line. See Methods for details on each technique.

Figure 2

BF STEM plan-view images of InP CELO grown on (100) InP substrates at different growth temperatures of (a) 630 °C, (b) 600 °C, (c) 570 °C, and (d) 550 °C. The samples (a), (b) grown at higher temperatures show {110} type side facets and {111} type end facets (plan-view STEM cannot distinguish between, for instance, ($1\overline{1}0$) and ($\overline{1}\overline{1}0$) or between ($1\overline{1}\overline{1}$)A and ($\overline{1}\overline{1}\overline{1}$)B. Hence, {110} or {111} is used). The samples (c), (d) grown at lower temperatures show rectangular overgrowths with primarily {111} type end facets. The orientation of all the samples is the same [as shown in (d)] and the direction of the template is along $\left[0\overline{11}\right]$.

Figure 3

InP CELO grown on (100) InP at 600 °C. (a) BF STEM image of the plan-view sample showing defective (light) and nondefective (dark) areas. White arrows (1,2) point to two relatively defect-free areas, arrow 3 points to a defect-dense area. (b) Shows the plan-view BF STEM of the other end of the same growth. (c) HAADF STEM of cross section taken along red line in (b) showing a (011) and a ($\overline{1}11$)B facet. (d) Cross-section STEM of the plan-view lamella in (a) taken along the red dashed line showing ($1\overline{11}$)A and ($\overline{211}$)B end facets. (e) STEM corresponding to the area marked by the yellow box in (a) showing a defect-free region (green) in between areas with high densities of SFs and twins (red). Inset shows a high-resolution STEM of the region marked by the black square. White arrow points to a stacking fault. (f) Three-dimensional (3D) visualization of the facets in this overgrowth.

Figure 4

InP CELO on InP (100) substrates grown at 570 °C. (a) BF STEM of a CELO structure showing defects as dark contrasts. (b) shows HAADF STEM of a cross-sectional cut taken along red dashed line in (a). In (a), (b) orange and white arrows show limits of defective and defect-free regions, respectively. Blue arrow marks SFs in the defective part. (c) shows a high-resolution cross-section STEM of the region marked by a blue box in (b). Inset shows Fourier transform with the streaks along [111] corresponding to the SFs. (d) shows cross-sectional STEM of the end facet marked by the blue box in (a). (e) shows a 3D visualization of the facets and orientation of the intersecting stacking fault planes. The inset shows the pair of intersecting SFs as seen when looking along the top gray arrow (plan view).

Figure 5

InP CELO growths on (100) InP substrate at 570 °C with different V/III ratios. (a), (b) show the top-view SEM (of a region with multiple CELO templates) and BF STEM of a representative structure, respectively, for a growth done at a high V/III ratio of 700. (c), (d) show the top-view SEM (of regions with multiple CELO templates) and BF STEM of a representative structure, respectively, for a growth done at low V/III ratio of 240. The scale bars in (a), (c) are both 10 μm. (e) shows a schematic top-down view representation of the change in faceting with temperature and V/III ratio. The insets show cross-section schematics of the facets observed, where the relative ratio of the facets varies. The arrows in (e) point to the growth direction out of the center seed hole.

Figure 6

Plan-view TEM micrographs analyzing growth in different orientations on a (100) InP substrate. (a) shows the HAADF STEM of the entire lamella with a flower pattern of CELO templates starting from the one oriented along [110] and with separations of 18 ° between consecutive templates. (b)–(f) BF STEM of individual templates oriented in different directions on the wafer. The nature and density of defects change as the orientations of the templates vary from [0 $\overline{11}$] to [0 $\overline{1}1$]. The white arrows point to the direction that the templates are oriented. (g) shows the total area of overgrown III-V materials in each of these templates and (h) shows the fraction of defect-free area in the different samples.

Figure 7

Plan-view TEM of InP CELO grown on InP(110) substrates. (a), (b) show representative growths in templates oriented along $\left[1\overline{1}0\right]$. (a) shows twinning along the {111}A planes (red dashed line); (b) shows perfect sharp {110} type vertical flat facets. (c) shows CELO growth in templates oriented along [100]. The growth towards $\langle 100\rangle$ orientation is terminated by a sharp {100} facet while the $\langle 00\overline{1}\rangle$ orientation is terminated by {111}B facets. There are edge twins on the side growing towards $\langle 001\rangle$. Twin planes are marked by blue dashed lines. (d) shows backscatter SEM of two different growths in templates oriented along [110]. The bright lines are InGaAs markers in between InP growths. (e) shows how the crystal facets on the growth plane are different depending on which orientation the crystal grows in. The red and blue planes represent the {111}A and {111}B planes, respectively. The Miller cubes shown correspond to how it would look when viewed along the corresponding arrows.