Fast Diffusion and Segregation along Threading Dislocations in

Subscriber access provided by Macquarie University

Communication

Fast diffusion and segregation along threading dislocations in semiconductor heterostructures Bastien Bonef, Rushabh Shah, and Kunal Mukherjee Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.8b03734 • Publication Date (Web): 11 Feb 2019 Downloaded from http://pubs.acs.org on February 12, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

Fast diffusion and segregation along threading dislocations in semiconductor heterostructures Bastien Bonef1, Rushabh D. Shah2, and Kunal Mukherjee1 1Materials Department, University of California, Santa Barbara, CA 93106, USA 2Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139 USA

Abstract. Heterogeneous integration of semiconductors combines the functionality of different materials and enables device technologies such as III-V lasers and solar cells on silicon and GaN LEDs on sapphire. However, threading dislocations generated during heteroepitaxy remains a key obstacle to the success of this approach due to reduced device efficiencies and reliability. Strategies of alleviating this and understanding carrier recombination must include a proper description of the structure and properties of threading dislocations, which has been lacking. To this end, we show that the composition around

threading

dislocations

in

as-grown

technologically

important

InGaAs/GaAs/Ge/Si

heterostructures are indeed different from that of the matrix. Defect-diffusion along the dislocation core that is orders of magnitude faster than bulk is responsible for this. We present evidence for the simultaneous diffusion of germanium and indium up and down the dislocation respectively leading to unique compositional profiles. We also detect the formation of clusters of metastable composition at the interface between Ge and GaAs enabled by intermixing in these two nearly immiscible materials. Site-specific atom probe tomography reveals these results in microscopic detail around individual dislocations enabled by electron channeling contrast imaging. Our results have important implications for the electronic and mechanical properties of dislocations and interfaces in semiconductors and point the way to strategies to passivate dislocations.

Keywords. Single dislocation; Atom probe tomography, Electron channeling contrast imaging, Fast diffusion; Site-specific extraction; Semiconductor heterostructure. 1

ACS Paragon Plus Environment

Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Dislocations are one-dimensional defects that strongly influence the mechanical and electronic properties of crystalline matter. In semiconductors, threading dislocations arising from the growth of thin films on dissimilar substrates limit device performance, their reliability, and ultimately their commercial viability1–4. The study of how dislocations impact crystal properties has matured to the point where it is now imperative to fully characterize the types of atoms that are present at the dislocation. This realization stems from the fact that dislocations can support compositions or defect equilibria distinct from the rest of the crystal in a variety of materials, and simple models of dangling crystal bonds in an otherwise uniform lattice do not explain the observed electronic behavior5–9. Further, dislocations also act as fast diffusion paths in crystals10,11 with recognized implications for silicon-based devices due to enhanced dopant diffusion12–14. This so-called “pipe diffusion” is usually studied as an enhancement in a spatially averaged bulk diffusion coefficient due to the presence of dislocations15–17, which does not capture the local inhomogeneity in composition. The local chemical environment of a dislocation in semiconductors not only affects its electronic properties18–21 but also its mechanical properties like glide motion22,23. A modification of the dislocation glide properties due to segregates have implications for the ultimate dislocation densities24 and reliability in classes of dislocation containing devices such as III-V lasers25,26. Atom probe tomography (APT) has been successfully used for the study of the local environment at dislocations primarily in metals, presenting direct three-dimensional views of segregation of impurities and even distinct structural phases at the core27–31. However, the volume of material sampled in atom probe is very small and the standard location-blind approach to APT is applicable for dislocation analysis only if the material has dislocation densities greater than 10101011/cm2. While this criterion is met for worked metals and damaged semiconductors, device-quality epitaxial semiconductor heterostructures with their low dislocation densities present significant experimental and statistical challenges for dislocation studies by APT. To improve the odds of capturing 2


Page 2 of 29

Page 3 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

a threading dislocation, here we use electron-channeling contrast imaging (ECCI) to locate threading dislocations in p-In0.01Ga0.99As/n-In0.05Ga0.95As/GaAs/Ge epitaxial layers on silicon substrates for subsequent APT analysis. The silicon substrate is offcut 6° from the [001] towards [111]. ECCI is a diffraction-based non-destructive scanning electron microscope (SEM) technique that uses backscattered electrons to identify extended crystal defects by their strain fields near the surface32,33. The sample studied here has an average dislocation density of 3x108/cm2, closer to realistic devices and orders of magnitude lower than that previously studied by APT in silicon and metals.

Tip preparation guided by channeling contrast microscopy and APT analysis. In order to know where to extract an APT tip in low dislocation density samples, it is important to see the dislocation. Figure 1a shows typical threading dislocations in the epitaxial p-In0.01Ga0.99As/n-In0.05Ga0.95As/GaAs/Ge layers (silicon substrate not shown) using bright-field transmission electron microscopy. The threading dislocation density is high enough that some threading dislocations can fuse to form dislocation junctions due to their inclination34. Unfortunately, secondary electron emission yield from the sample during conventional focused ion beam (FIB) APT tip preparation is insensitive to dislocations. Figure 1b shows this lack of dislocation contrast in secondary electron images. ECCI, on the other hand, shows strong contrast from threading dislocations as seen in Figure 1c for the same region. This allows for the identification of a site (labeled in Figure 1c) from which to extract an APT tip that has a high probability of containing a dislocation. In our case, ECCI and FIB-APT tip preparation were not available on the same electron microscope. Hence, the micron-sized growth void in the center of the image serves as a fiducial marker to locate this site. Note that as a typical APT tip radius is only 50 nm, a threading dislocation density > 1.3×1010/cm2 is normally required to capture on average one threading dislocation per tip prepared from a random site. We note that ECCI can inform APT locations beyond threading

3


Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 29

dislocations, as it is sensitive to deviations in the lattice caused by a variety of extended defects such as misfit dislocations, stacking faults, and grain boundaries.

Identification of threading dislocations by enriched structures. Figure 2a shows the three dimensional APT reconstruction of the tip, prepared from the marked site in Figure 1c. Here, the layer thicknesses and interface flatness was used to verify the integrity of the reconstruction (see experimental section). We can clearly resolve the p-In0.01Ga0.99As, n-In0.05Ga0.95As, and GaAs layers in the heterostructure. We do not see the underlying germanium layer as the APT tip fractured in the process of evaporating the GaAs layer. Figures 2b and 2c respectively show the distribution of germanium and indium atoms in the GaAs layer and the n-In0.05Ga0.95As layer in the same view as in Figure 2a. These views show regions of enriched indium and germanium arranged in vertically oriented lines. As we will show, the nature of these lines are highly suggestive of their origins in dislocations. Two indium-enriched lines in Figure 2c appear to be close to merging near the n-In0.05Ga0.95As/GaAs interface. In the same region, Figure 2b shows a third line of enriched germanium that extends further up into the In0.05Ga0.95As layer. This enriched segment exits the APT tip before intersecting with the In0.01Ga0.99As layer. The bottom of Figure 2b also shows significant amounts of germanium atoms in the GaAs layer not arranged in lines but as clusters. We first take a closer look at the enriched lines of indium and germanium, followed by a short discussion of the germanium clusters towards the end of this paper. We find that the two indium-enriched segments are nearly co-planar and can be mostly captured in a single 2 nm thick vertical slice. We rotate the sample to view this plane face-on and label this view as 0°. Likewise, the germanium-enriched segment in the In0.05Ga0.95As layer also lies on a single plane and can be wholly captured in a 2 nm vertical slice only after rotating the sample by 90° from the 4


Page 5 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

first view. Figures 3a,b and Figures 3c,d, respectively, show these two views (0° and 90°) for indium and germanium concentrations. Here, we only show maximal projections through the entire thickness of the APT tip for clarity. We obtain this by displaying only the maximum atom concentration (using a 2×2×2 nm3 grid) along each column perpendicular to the plane of the view. The angle between the two indiumenriched segments is ≈70⁰, and the angle of these segments to the GaAs/Ge interface is ≈58⁰ and ≈52⁰, respectively. While we note that these angles are approximate and limited by the accuracy of the reconstruction, they are consistent with expectations from threading dislocations in III-V zincblende films that lie on (111) planes on an offcut substrate. Specifically, these angles suggest a line direction of that makes an angle 54.7⁰ with a (001), but further tilted by approximately ±3⁰ due to the substrate offcut of 6⁰. The angle between two (111) glide planes is 70.4°. Figure 3a shows these exact angles for comparison with the enriched indium segments. Using this, we identify view 0° as the [110] projection. It is the remarkable straightness of many parts of the dislocation allows for this analysis. This is due to high Peierls barriers in semiconductors as compared to metals, leading to dislocations aligning to defined crystallographic directions. Hence, while it is common in the APT of semiconductors to lose crystallographic information during evaporation35–38, an inspection of angles between the enriched lines and that to the flat interfaces allows us to recover some of this information and presents a picture consistent with them being dislocations. While confined to the (111) slip plane, threading dislocations in the III-V zincblende system have some freedom in the line direction on this slip plane. They can minimize their line tension by balancing their line direction (screw/edge nature) and their total length in the film. It appears that the dislocations choose an approximate orientation on this plane, in agreement with prior expectations39. An arrow marks the location of what we think is a 10 nm jog in one of the threading dislocations,

5


Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 29

remarkably well preserved in the indium-enriched data. Here the dislocation shifts to a parallel glide plane, likely to minimize further the length of the threading segment in the thin film. Our data suggests that it is very likely that the threading dislocations captured in the APT tip represent a dislocation fusion reaction—the two threading dislocations best noted by indiumenrichment fuse together to form a single threading dislocation that is best seen by germaniumenrichment. Such reactions are common in heteroepitaxial films and represent an important mechanism for threading dislocation density reduction with increasing film thickness39. The dislocation switches into another slip plane after fusion as such reactions conserve the total Burgers vector. Accordingly, we find that it is no longer possible to see the complete resultant threading dislocation after fusion in this or any single thin slice parallel to view 0° due to a change in line direction out of this plane. Figure 3e shows a simple schematic of this fusion reaction showing the two views and the switch in the {111} glide plane after fusion, leading to the entire fused dislocation captured in a single vertical slice only along view 90°. The fused dislocation line direction has an inclination that is on average greater than 54.7° (corresponding to ) to the interface, indicating that the dislocation is not entirely contained within a single (111) plane but rather might have several jogs as well which cannot be individually resolved. However, some straight segments are indeed close to 54.7°. Thus from this simple analysis of the geometry, we are able to say that the enriched germanium and indium lines correspond to dislocations that are typical in III-V materials. We have captured a wellknown dislocation fusion process in our APT tip. This implies that the following measurements of the composition at dislocations although hitherto uncharacterized should also be considered typical of such materials.

6


Page 7 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

Composition at threading dislocations. A mass spectrum showing Ge2+ and In+ peaks extracted from the In0.05Ga0.95As layer is provided in supporting Figure S-1a. It demonstrates the ability of APT to resolve germanium and indium enrichment in arsenide semiconductors. Nonetheless, we emphasize that absolute quantification by APT remains a challenge, discussed further in supporting information S-2. Briefly, local magnification artifacts arising from the simultaneous evaporation of two adjacent phases (such as a Ge-containing dislocation core in a GaAs matrix) with different evaporation fields can lead to trajectory artifacts for the ions leaving the tip surface40,41. These artifacts, coupled with the spatial resolution limits of laser pulsed APT, can lead to errors in quantification of concentration profiles. In this work, we expect that germanium composition might be underestimated because of this effect; therefore, our values serve as a lower bound for concentrations and a higher bound for lateral diffusivities. Vertical composition profiles. Figure 4a shows a 2D concentration profile of indium along one of the two dislocation segments in GaAs layer only. We attribute this enrichment to downward diffusion of indium from the InGaAs layer along the dislocation. An nearly constant indium concentration of 0.3–0.6 at.% is measured in the dislocation segment in the GaAs layer despite complete miscibility of InAs in GaAs at these growth temperatures. Figure 4b shows a 2D concentration profile of germanium along the dislocation segment. The germanium atoms segregate at the dislocation segments in both the GaAs and In0.05Ga0.95As layers. Given that germanium is not a constituent element in the III-V layers, upward diffusion from the germanium layer is the most likely scenario for this segregation. The measured concentration of germanium at the dislocation segment in the In0.05Ga0.95As layer is 0.2–0.3 at.% and is comparable to the bulk solid solubility of germanium in GaAs42. The interference from germaniumcontaining clusters makes it difficult to isolate the behavior of germanium along the two dislocation segments in the GaAs layer; however, a qualitatively similar level of segregation exists. 7


Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

We estimate the dislocation diffusivity from an analysis of the concentration gradient of the solute along the dislocation. We are actually able to see the starting point of downward indium dislocation diffusion at the intersection of the threading dislocation and the In0.05Ga0.95As/GaAs interface. Figure 4c shows the transition in indium composition at this starting point, both along the dislocation core and in the matrix away from the dislocation core. As expected, there is a sharp drop in the indium concentration of the matrix at the interface. This is due to low bulk interdiffusivity in III-V materials. However, there is a drop in the indium concentration at the interface measured along the threading dislocation as well where interdiffusivity should be enhanced. The origin of the drop along the dislocation could lie in strain-limited solubility at the core in what are otherwise miscible materials. As an example, if the matrix around the dislocation remains GaAs, the amount of indium that can be present at the core could be limited due to the introduction of compressive strain following diffusion. This would lead to an equilibrium solubility (constant source) of indium in GaAs at the start of diffusion in the core. Right after the drop across the interface along the dislocation, there is a very small concentration gradient. We tentatively estimate a diffusivity of 10-14/cm2 by a fit to a constant source diffusion condition in one dimension. While there are no comparable bulk diffusivity experiments, this value is four orders of magnitude faster than bulk lattice diffusivity at these temperatures estimated at In0.05Ga0.95As/GaAs interfaces after separately factoring in the impact of n-type doping43 and extrapolating for temperature44. Surprisingly, there is no overall germanium concentration gradient in the growth direction along the 150 nm length of the defect; the solid solubility appears to limit the composition. Treating the problem in one dimension, this implies that the germanium dislocation diffusivity in In0.05Ga0.95As is greater than 10-12cm2/s (resulting in a flat profile to within 10%). This is five orders of magnitude faster than postgrowth bulk lattice-diffusivity in GaAs measured by thin film intermixing45 and two orders of magnitude 8


Page 8 of 29

Page 9 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

faster than near-surface lattice-diffusivity seen during GaAs on germanium epitaxy at the same temperature46. Lateral composition profiles. In addition to fast diffusion along the core, we expect that indium and germanium will diffuse laterally out of the core via bulk diffusion. We do not perform an analysis of lateral diffusion for indium out of the core in the GaAs layer as the indium-enriched dislocation segments are not very straight. The diffuse 2D indium profile in Figure 4a points to this. Nevertheless, we note one very important finding. We do not see enrichment of indium to the threading dislocation in the In0.05Ga0.95As layer. Figure 4d shows this more clearly in the proximity histogram collected from Site A, a straight segment of the dislocation in the In0.05Ga0.95As layer. The previously discussed segregation of germanium is clearly visible but the indium appears to be unaffected. The source of any indium segregation in this case would have likely been via adatom diffusion on the growth surface. We do not see this to within experimental limit. This is in contrast to reports of indium segregation to threading dislocations seen in InGaN materials by electron microscopy47,48. The straighter segments of dislocation in the In0.05Ga0.95As layers allows us to investigate lateral diffusion of germanium. Figure 4e shows a cross-sectional radial profile of germanium concentration at the dislocation in the In0.05Ga0.95As layer, averaged over 3 nm along the length of the dislocation. Even here, the dislocation line is not perfectly straight and averaging over thicker segments leads to a smearing of the profile. In this preliminary assessment, the profile can be separated into a region with a radius of about 1 nm where the concentration appears to plateau and a bulk region beyond that with a concentration gradient that extends out to nearly 10 nm from the center. Here, we think that this concentration gradient is likely to be a result of lateral germanium lattice-diffusion out of a ‘constantsource’ fast-diffusivity core region. Ideally, APT should be well suited examining these features around a dislocation. This is important as there is debate about whether the size of this region is strictly limited to 9


Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 29

within a Burgers vector from the core or if it extends somewhat beyond10,49. Further, if the dislocation is dissociated as they usually are in semiconductors, it is not clear whether the connecting stacking fault is also a region of fast diffusivity50. Unfortunately, the quantification artifacts previously mentioned and the poorer lateral spatial resolution of laser pulsed APT complicates this analysis for semiconductors. Considering these errors, our measurements are a rough upper estimate for the actual lateral diffusivity and the size of the fast diffusivity region. We are able to obtain a bulk lattice-diffusivity of approximately 10-16 cm2/s by fitting our measured profile to an approximate analytical solution for constant source diffusion out of a cylindrical region of radius 1 nm51. This value is in good agreement with prior reports of bulk lattice-diffusivity in Ge/GaAs45 and this situation corresponds to a Harrison Type C-kinetics regime of short-circuit diffusion with non-overlapping lateral diffusion profiles between neighboring dislocations52. Coexistence of indium and germanium at the dislocation. Figure 4f shows cross-sectional 2D projections of germanium and indium concentrations taken along the dislocation on either side of the GaAs/In0.05Ga0.95As interface. These maps are averaged over a 13 nm thickness along the dislocation line direction, which leads to some profile broadening. As the germanium diffuses up and the indium diffuses down, we find that both species coexist at the dislocation segment in the GaAs layer. In particular, we note the coexistence configuration is one where germanium occupies a region slightly displaced from that of indium. This could be a size effect. Indium has a ≈17% larger covalent tetrahedral radii than the nearly equally sized germanium and gallium and could preferentially occupy the tensile strained core region of the dislocation. However, germanium is an amphoteric dopant in GaAs and electrostatic effects could be in play. Further, we cannot completely rule out glide or climb of the threading dislocation segment itself as the film is growing. This could also lead to complicated lateral

10


Page 11 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

composition profiles. These artifacts coupled with the limited lateral spatial resolution of the laser pulsed APT prevents a more detailed analysis of this spatial distribution.

Ge-containing clusters in GaAs. In addition to dislocations, intermixing phenomena at nearly immiscible semiconductor interfaces have also not received much attention in APT studies and the lattice-matched GaAs/Ge interface is a prototypical example of such an interface. We note the unexpected presence of a large number of germanium-containing clusters in the GaAs layers in Figures 2b and 3c-d that at first glance seem unconnected to the dislocation. The clusters are seen as high as 100 nm from the GaAs/Ge interface. A second APT tip without dislocations is prepared from a random area of the sample. Figures 5a and 5b show the pristine 3D reconstruction and maximum concentration projections, respectively, from this tip, now showing the Ge/GaAs interface clearly. We see that similar germanium-containing clusters are also present in regions that do not contain dislocations. The clusters are ≈5 nm wide but exist only up to a height of 40 nm from the GaAs/Ge interface in the second tip. Figures 5c, 5d, and 5e shows proximity histograms53 measured from germanium iso-surfaces54 drawn around the clusters marked as sites B, C, and D, respectively, in Figure 3d (sites B and C) and Figure 5b (site D). We see that in all cases the arsenic concentration is unchanged going from the GaAs matrix to the clusters, suggesting that the intermixing only occurs on the group-III sublattice and the clusters remain zincblende. Considering the evaporation artifacts mentioned previously, the germanium concentration at the core of the clusters measured in Figure 5(c-e) might be underestimated. Nevertheless, qualitatively, the observed trend of increasing germanium concentration from site A to site D is valid. These compositions of (Ge,Ga)As are metastable and are among the highest germanium-containing zincblende 11


Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 29

alloys known, possibly stabilized by their small volume and the surrounding GaAs matrix. Germanium is known to diffuse into GaAs fairly rapidly at typical sample growth temperatures55. We speculate that as we cool the sample to room temperature, the bulk solubility limit of germanium in GaAs decreases leading to a driving force for the excess germanium to cluster. Enhanced diffusion at threading dislocations transports germanium higher into the GaAs layer, explaining why germanium-containing clusters are found significantly higher in the III-V layers near the dislocation. It is possible that this transport also leads to clusters further from the interface to have a lower concentration of germanium. Overall, these results provide insight into the microstructure of immiscible semiconductor interfaces. While GaAs/Ge interfaces have recently been used in multijunction solar cells, such devices56 do not yet directly incorporate this interface in the active region due to issues with doping. More work is necessary in order to understand the properties of these metastable clusters on the electrical properties of the interface.

Conclusions. The composition of a dislocation in a semiconductor is expected to play an important role in determining both its mechanical and electronic properties. In this work, we show that fast diffusion operates along threading dislocations in conventional III-V semiconductor heterostructures at growth temperatures, leading to significant intermixing along the dislocation core. We note that ECCI complements the APT analysis of crystalline defects and phase transformations particularly well and has a promising role to play in semiconductor materials characterization. Using ECCI and APT, we provide a detailed microscopic view of segregation and diffusion in dislocations in technologically relevant materials, but the discussion remains somewhat qualitative due to the complexity of charged solute interactions in semiconductors coupled with potential APT artifacts. The dislocation diffusion of both a dopant (germanium) and an isovalent atom (indium) is noted to be orders of magnitude above that of 12


Page 13 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

lattice-diffusion in GaAs. Thus short-circuit diffusion of atoms along dislocations has to be factored in together with lateral segregation when discussing lattice-mismatched semiconductors. While any deviation in local composition is detrimental to device uniformity, it remains to be quantified to what extent, if at all, such intermixing modifies carrier recombination at dislocations. These results now point the way to the tailoring of the properties of dislocations by intentional diffusion of foreign atoms57,58.

Experimental Section. Sample synthesis. The epitaxial films were grown in a Thomas Swan/Aixtron coldwalled 6×2″ MOCVD reactor with a close-coupled showerhead configuration. The precursors used to grow the films are SiH4, GeH4, TMGa, TMIn, AsH3 for silicon, germanium, gallium, indium, and arsenic respectively. Si2H6, CBrCl3 are used as precursors for doping InGaAs n+ and p+ respectively. A 1 µm germanium layer was first grown on a vicinal (001) silicon substrate with a 6 degree miscut towards (111) with a thin low temperature germanium nucleation buffer layer at 400 ⁰C. This was followed by growth at 600 ⁰C to produce a strain relaxed film with a moderate dislocation density59,60. GaAs was then grown with a high AsH3 partial pressure nucleation layer at 625 ⁰C61 to suppress anti-phase domains. For the In0.01Ga0.99As/In0.05Ga0.95As layers, flow rates for the indium and gallium precursors are kept constant at 6.4 μmoles.min-1 and 130 μmoles.min-1 respectively with a V/III ratio of 65. The growth temperature is kept at 600 ⁰C to allow for high C incorporation for p+ doping62,63. The growth rates for the III-V layers range between 0.5-0.6 nm.sec-1. Dislocation analysis by electron microscopy. A cross-section transmission electron microscopy (TEM) sample was assembled and thinned down to 10-20 µm using a disc grinder. Further thinning to electron transparency is performed by broad Ar-ion beam milling with GATAN precision ion polishing system. The cross-section imaging of the sample was performed using a JEOL JEM-2011 TEM operated at 200 kV. The sample was tilted off the [110] zone axis to a two-beam condition with g=[-220]. Bright field 13


Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 29

(BF) images are taken to highlight the dislocations. The presence and the location of dislocations in the sample were noted in plan-view using electron channeling contrast imaging (ECCI) in a FEI Quanta 400f. The microscope is operated at 30 kV with a probe current of 3 nA and at a working distance of 6 mm. ECCI is performed using a pole-piece mounted solid-state backscatter detector with the specimen aligned to a three-beam (g=022,004) channeling condition. APT analysis. The APT specimen was prepared using a dual FEI Helios 600 focused ion beam (FIB) also equipped for SEM. A 2x2 µm2 platinum protection layer is centered 1.4 µm away from the fiducial. Standard preparation procedure is performed to extract the region of interest with the annular milling patterns used for tip sharpening carefully centered on top of the platinum protection layer64. A final milling performed at 2 kV is performed to minimize gallium-induced damage and remove the remaining platinum. The extracted APT sample was analyzed in a Cameca 3000X HR local electrode atom probe (LEAP) operated in laser-pulse mode. The tip was cooled down to a temperature of 50 K. The laser illuminated the tip at a wavelength of 532 nm with an energy of 0.8 nJ, focused on a ∼10 μm wide spot and at a repetition frequency of 200 kHz. The ion detection rate was kept at 0.02 ions.pulse-1 by adjusting the DC voltage applied on the specimen. The 3D reconstruction of the analyzed volume has been performed using commercial software IVASTM and by applying the cone angle/initial tip radius protocol65. The layer thicknesses measured in TEM (Figure 1a) were used as references for the optimization of the reconstruction66. As a result, the n-In0.05Ga0.95As layer is 200 nm thick in the APT tip, measured using a 1D-concentration profile perpendicular to the interfaces between the layers. This is in very good agreement with the thickness measured by TEM. Moreover, we iteratively optimized the 3D reconstruction parameters until both the p-In0.01Ga0.99As/n-In0.05Ga0.95As and n-In0.05Ga0.95As/GaAs interfaces were flat. This ensure a reliable reconstruction in the x-y, and z-directions. Local composition in the APT reconstructions were obtained by subdividing the volumes in 0.5×0.5×0.5 nm3 voxels. Atoms 14


Page 15 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

contribute to the calculation of compositions in each voxels using a Gaussian delocalization algorithm67. The broadening parameters σx, σy, and σz in each direction were set to 1.5 nm68. The respective germanium concentration used to drawn the iso-surfaces around Site A to C are 0.01%, 0.1%, 0.1% and 2%. Acknowledgements This work was supported in part by the National Science Foundation through the MRSEC Program of the National Science Foundation through Grant No. DMR-1720256 (Seed Program). This study made use of the Substrate Engineering Laboratory and the MRSEC Shared Experimental Facilities at MIT, partly supported by the National Science Foundation under Grant No. DMR-14-19807. Funding for B. Bonef was provided by the Solid State Lighting & Energy Electronics Center. Supporting information Supporting information S-1 is an APT mass spectrum showing the germanium identification in a dislocation. Supporting information S-2 is an illustration of trajectory aberrations artifacts in atom probe tomography from the simulation package 2D Field Evaporation Simulator implemented in IVASTM. References (1)

Fitzgerald, E. A. Mater. Sci. Reports 1991, 7, 87–140.

(2)

Kozodoy, P.; Ibbetson, J. P.; Marchand, H.; Fini, P. T.; Keller, S.; Speck, J. S.; DenBaars, S. P.; Mishra, U. K. Appl. Phys. Lett. 1998, 73, 975–977.

(3)

Liu, A. Y.; Zhang, C.; Norman, J.; Snyder, A.; Lubyshev, D.; Fastenau, J. M.; Liu, A. W. K.; Gossard, A. C.; Bowers, J. E. Appl. Phys. Lett. 2014, 104, 041104.

(4)

Richardson, C. J. K.; Lee, M. L. MRS Bull. 2016, 41, 193–198.

(5)

Ourmazd, A. Contemp. Phys. 1984, 25, 251–268.

(6)

Fell, T. S.; Wilshaw, P. R.; De Coteau, M. D. Phys. Status Solidi 1993, 138, 695–704. 15


Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 29

(7)

Hierro, A.; Hansen, M.; Zhao, L.; Speck, J. S.; Mishra, U. K.; DenBaars, S. P.; Ringel, S. A. Phys. status solidi 2001, 228, 937–946.

(8)

Mukherjee, K.; Reilly, C. H.; Callahan, P. G.; Seward, G. G. E. J. Appl. Phys. 2018, 123, 165701.

(9)

Hirsch, P. B. Mater. Sci. Technol. 1985, 1, 666–677.

(10)

Balluffi, R. W. Phys. status solidi 1970, 42, 11–34.

(11)

Legros, M.; Dehm, G.; Arzt, E.; Balk, T. J. Science. 2008, 319, 1646–1649.

(12)

Barson, F.; Hess, M. .; Roy, M. J. Electrochem. Soc. 1969, 116, 304–307.

(13)

Braga, N.; Buczkowski, A.; Kirk, H. R.; Rozgonyi, G. A. Appl. Phys. Lett. 1994, 64, 1410–1412.

(14)

Fiorenza, J. G.; Braithwaite, G.; Leitz, C.; Currie, M. T.; Cheng, Z. Y.; Yang, V. K.; Langdo, T.; Carlin, J.; Somerville, M.; Lochtefeld, A.; et al. In 2004 IEEE International Reliability Physics Symposium. Proceedings; 2004; pp. 493–497.

(15)

Campbell, D. R.; Tu, K. N.; Schwenker, R. O. Thin Solid Films 1975, 25, 213–220.

(16)

Kim, Y.; Kim, M. S.; Min, S.; Lee, C. J. Appl. Phys. 1991, 69, 1355–1358.

(17)

Christensen, J. S.; Kuznetsov, A. Y.; Gunnaes, A. E.; Svensson, B. G.; Radamson, H. H. Phosphorus Mater. Sci. Semicond. Process. 2006, 9, 650–654.

(18)

Titchmarsh, J. M.; Booker, G. R.; Harding, W.; Wight, D. R. J. Mater. Sci. 1977, 12, 341–346.

(19)

Yamaguchi, M.; Amano, C. J. Appl. Phys. 1985, 58, 3601–3606.

(20)

Donolato, C. J. Appl. Phys. 1998, 84, 2656–2664.

(21)

Speck, J. S.; Rosner, S. J. Phys. B Condens. Matter 1999, 273–274, 24–32.

(22)

Yonenaga, I.; Sumino, K. J. Appl. Phys. 1987, 62, 1212–1219.

(23)

Burle-Durbec, N.; Pichaud, B.; Minari, F. Philos. Mag. Lett. 1989, 59, 121–129.

(24)

Beanland, R.; Dunstan, D. J.; Goodhew, P. J. Adv. Phys. 1996, 45, 87–146.

(25)

Yellen, S. L.; Shepard, A. H.; Dalby, R. J.; Baumann, J. A.; Serreze, H. B.; Guido, T. S.; Soltz, R.; Bystrom, K. J.; Harding, C. M.; Waters, R. G. IEEE J. Quantum Electron. 1993, 29, 2058–2067.

(26)

Jung, D.; Norman, J.; Wan, Y.; Liu, S.; Herrick, R.; Selvidge, J.; Mukherjee, K.; Gossard, A. C.; Bowers, J. E. Phys. status solidi 2019, 216, 1800602.

(27)

Blavette, D.; Cadel, E.; Fraczkiewicz, A.; Menand, A. Science. 1999, 286, 2317–2319.

(28)

Miller, M. K. Microsc. Res. Tech. 2006, 69, 359–365.

(29)

Thompson, K.; Flaitz, P. L.; Ronsheim, P.; Larson, D. J.; Kelly, T. F. Science 2007, 317, 1370–1374.

(30)

Kuzmina, M.; Herbig, M.; Ponge, D.; Sandlobes, S.; Raabe, D. Science. 2015, 349, 1080–1083. 16


Page 17 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

(31)

Bonef, B.; Grenier, A.; Gerard, L.; Jouneau, P.-H.; André, R.; Blavette, D.; Bougerol, C. Appl. Phys. Lett. 2018, 112, 093102.

(32)

Simkin, B. .; Crimp, M. Ultramicroscopy 1999, 77, 65–75.

(33)

Picard, Y. N.; Liu, M.; Lammatao, J.; Kamaladasa, R.; De Graef, M. Ultramicroscopy 2014, 146, 71– 78.

(34)

Romanov, A. E.; Pompe, W.; Beltz, G.; Speck, J. S. Geometry and Crystallography. Phys. status solidi 1996, 198, 599–613.

(35)

Bonef, B.; Catalano, M.; Lund, C.; Denbaars, S. P.; Nakamura, S.; Mishra, U. K.; Kim, M. J.; Keller, S. Appl. Phys. Lett. 2017, 110, 143101.

(36)

Müller, M.; Gault, B.; Field, M.; Sullivan, G. J.; Smith, G. D. W.; Grovenor, C. R. M. Appl. Phys. Lett. 2012, 100, 2010–2014.

(37)

Bonef, B.; Gérard, L.; Rouvière, J.-L.; Grenier, A.; Jouneau, P.-H.; Bellet-Amalric, E.; Mariette, H.; André, R.; Bougerol, C. Appl. Phys. Lett. 2015, 106, 051904.

(38)

Megalini, L.; Bonef, B.; Cabinian, B. C.; Zhao, H.; Taylor, A.; Speck, J. S.; Bowers, J. E.; Klamkin, J. Appl. Phys. Lett. 2017, 111, 032105.

(39)

Speck, J. S.; Brewer, M. A.; Beltz, G.; Romanov, A. E.; Pompe, W. J. Appl. Phys. 1996, 80, 3808– 3816.

(40)

Vurpillot, F.; Bostel, A.; Blavette, D. Appl. Phys. Lett. 2000, 76, 3127.

(41)

Vurpillot, F.; Larson, D.; Cerezo, A.; Larson, D. J.; REINHARD, D. A.; KELLY, T. F.; Prosa, T.; Yao, L.; Cairney, J. M.; Ringer, S. P. Surf. Interface Anal. 2004, 36, 552–558.

(42)

Kolm, C.; Kulin, S. A.; Averbach, B. L. Phys. Rev. 1957, 108, 965–971.

(43)

Li, W. M.; Cohen, R. M.; Simons, D. S.; Chi, P. H. Appl. Phys. Lett. 1997, 70, 3392–3394.

(44)

Gillin, W. P.; Dunstan, D. J.; Homewood, K. P.; Howard, L. K.; Sealy, B. J. J. Appl. Phys. 1993, 73, 3782–3786.

(45)

Sarma, K.; Dalby, R.; Rose, K.; Aina, O.; Katz, W.; Lewis, N. J. Appl. Phys. 1984, 56, 2703–2707.

(46)

Hu, W.; Cheng, B.; Xue, C.; Su, S.; Liu, Z.; Li, Y.; Wang, Q.; Wang, L.; Liu, J.; Ding, J.; et al. Thin Solid Films 2012, 520, 5361–5366.

(47)

Massabuau, F.; Rhode, S.; Horton, M.; O’Hanlon, T.; Kovacs, A.; Zielinski, M.; Kappers, M. J.; Dunin-Borkowski, R.; Humphreys, C. J.; Oliver, R. A.; et al. In Gallium Nitride Materials and Devices XIII; Chyi, J.-I.; Morkoç, H.; Fujioka, H., Eds.; SPIE, 2018; Vol. 10532, p. 26.

(48)

Horton, M. K.; Rhode, S.; Sahonta, S.-L.; Kappers, M. J.; Haigh, S. J.; Pennycook, T. J.; Humphreys, C. J.; Dusane, R. O.; Moram, M. A. Nano Lett. 2015, 15, 923–930.

(49)

Picu, R. C.; Zhang, D. Acta Mater. 2004, 52, 161–171. 17


Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 29

(50)

Zhang, X.; Lu, G. Phys. Rev. B 2010, 82, 012101.

(51)

Crank, J. Oxford University Press: Oxford, 1980.

(52)

Harrison, L. G. Trans. Faraday Soc. 1961, 57, 1191–1197.

(53)

Hellman, O. C.; Vandenbroucke, J. A.; Rüsing, J.; Isheim, D.; Seidman, D. N. Microsc. Microanal. 2000, 6, 437–444.

(54)

Cairney, J. M.; Rajan, K.; Haley, D.; Gault, B.; Bagot, P. A. J.; Choi, P.-P.; Felfer, P. J.; Ringer, S. P.; Marceau, R. K. W.; Moody, M. P. Ultramicroscopy 2015, 159, 324–337.

(55)

Galiana, B.; Rey-Stolle, I.; Algora, C.; Volz, K.; Stolz, W. Appl. Phys. Lett. 2008, 92, 152102.

(56)

Karam, N. H.; King, R. R.; Haddad, M.; Ermer, J. H.; Yoon, H.; Cotal, H. L.; Sudharsanan, R.; Eldredge, J. W.; Edmondson, K.; Joslin, D. E.; et al. Sol. Energy Mater. Sol. Cells 2001, 66, 453–466.

(57)

Zhang, L.; McMahon, W. E.; Wei, S.-H. Appl. Phys. Lett. 2010, 96, 121912.

(58)

Wang, G.; Ogawa, T.; Soga, T.; Jimbo, T.; Umeno, M. Appl. Phys. Lett. 2001, 78, 3463–3465.

(59)

Lee, K. H.; Tan, Y. H.; Jandl, A.; Fitzgerald, E. A.; Tan, C. S. J. Electron. Mater. 2013, 42, 1133–1139.

(60)

Lee, K. H.; Jandl, A.; Tan, Y. H.; Fitzgerald, E. A.; Tan, C. S. AIP Adv. 2013, 3, 092123.

(61)

Kohen, D.; Bao, S.; Lee, K. H.; Lee, K. E. K.; Tan, C. S.; Yoon, S. F.; Fitzgerald, E. A. J. Cryst. Growth 2015, 421, 58–65.

(62)

Heidelberger, C.; Fitzgerald, E. A. J. Cryst. Growth 2016, 446, 7–11.

(63)

Buchan, N. I.; Kuech, T. F.; Scilla, G.; Cardone, F. J. Cryst. Growth 1991, 110, 405–414.

(64)

Thompson, K.; Lawrence, D.; Larson, D. J.; Olson, J. D.; Kelly, T. F.; Gorman, B. Ultramicroscopy 2007, 107, 131–139.

(65)

Vurpillot, F.; Gault, B.; Geiser, B. P.; Larson, D. J. Ultramicroscopy 2013, 132, 19–30.

(66)

Herbig, M.; Choi, P.; Raabe, D. Ultramicroscopy 2015, 153, 32–39.

(67)

Hellman, O. C.; Du Rivage, J. B.; Seidman, D. N. Ultramicroscopy 2003, 95, 199–205.

(68)

Torres, K. L.; Daniil, M.; Willard, M. A.; Thompson, G. B. Ultramicroscopy 2011, 111, 464–468.

Figures

18


Page 19 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

Figure 1. (a) Cross-sectional TEM image of the semiconductor heterostructure showing pIn0.01Ga0.99As/n-In0.05Ga0.95As/GaAs/Ge layers deposited on silicon substrate (not seen). A two-beam g= diffraction condition is used. Threading dislocations are seen in the Ge/GaAs/InGaAs interfaces. (b) Plan view SEM image of the surface of the sample from a different area. (c) Corresponding plan view electron channeling contrast image (ECCI) where threading dislocations are seen as dots. The site chosen for APT analysis is also shown here. The micron-sized growth defect is used as a fiducial marker since ECCI and APT preparation were performed on different microscopes.

19


Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 29

Figure 2. (a) 140x140x465 nm3 3D APT reconstruction showing the p-In0.01Ga0.99As, n-In0.05Ga0.95As and the GaAs layers. 4%, 100%, 0.1% and 0.1% of the indium, germanium, gallium and arsenic detected atoms, respectively, are shown. (b) 140x140x250 nm3 sampling volume extracted in the GaAs layer and the n-In0.05Ga0.95As layer in (a) showing germanium atoms and their diffusion along the dislocation. 100% of the Ge atoms are shown. (c) 140x140x107 nm3 sampling volume extracted from the GaAs layer in (a) showing the diffusion of indium along two dislocations. 100% of the indium atoms are shown.

20


Page 21 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

Figure 3. (a-d) Maximal projections along the APT tip showing enriched linear features corresponding to dislocations. For this, the maximum concentration values from a 2×2×2 nm3 interpolated grid is projected into the plane of display. The indium and germanium maps are shown in blue and red respectively. Angles are guides to the eye showing reasonable agreement between typical dislocations in III-V materials and the APT data. Sites A-C are used for proximity histogram measurements in Figure 4 and 5. (e) Approximate diagram of the geometry of the dislocation fusion reaction as interpreted from the APT data.

21


Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 29

Figure 4. (a) Indium composition measured along the dislocation in the GaAs layer. (b) Germanium composition measured along the dislocation in the In0.05Ga0.95As layer. (c) Indium composition across the In0.05Ga0.95As/GaAs interface measured along the dislocation and in the matrix (away from the dislocation). The solid line is a fit to diffusion in one dimension from a constant source. (d) Composition profiles in the vicinity of the dislocation in the In0.05Ga0.95As layer labeled A in Figure 3d. Values of distances above 0 correspond to the inside of the germanium-rich regions while values below 0 correspond to the outside. We see no evidence of indium segregation in this layer. (e) Lateral outdiffusion of germanium averaged over a 3 nm straight section of dislocation in the InGaAs layer. The concentration is normalized to that in the core (Ccore Ge). The solid line is a fit to an approximate solution to radial diffusion out of a cylindrical surface of constant composition Ccore Ge with a radius of 1 nm. (f) Indium and germanium composition profiles along the threading dislocation averaged over 13 nm thick slabs taken just above and below the In0.05Ga0.95As/GaAs interface. Germanium atoms in the GaAs layer are seen to be slightly displaced from the indium atoms. 22


Page 23 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

Figure 5. (a) A 100x100x140 nm3 3D APT reconstruction of a tip prepared from a region without dislocations. 100% of the Germanium atoms are shown. (f) Germanium-rich clusters seen in a maximal projection. Respective composition profiles in the vicinity of three germanium rich clusters labeled Site B (c), Site C (d) and Site D (e) in Figure 3d and 5b. Values of distances above 0 correspond to the inside of the Germanium rich clusters while values below 0 correspond to the outside.

23


Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 1. (a) Cross-sectional TEM image of the semiconductor heterostructure showing p-In0.01Ga0.99As/nIn0.05Ga0.95As/GaAs/Ge layers deposited on silicon substrate (not seen). A two-beam g= diffraction condition is used. Threading dislocations are seen in the Ge/GaAs/InGaAs interfaces. (b) Plan view SEM image of the surface of the sample from a different area. (c) Corresponding plan view electron channeling contrast image (ECCI) where threading dislocations are seen as dots. The site chosen for APT analysis is also shown here. The micron-sized growth defect is used as a fiducial marker since ECCI and APT preparation were performed on different microscopes. 110x51mm (300 x 300 DPI)


Page 24 of 29

Page 25 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

Figure 2. (a) 140x140x465 nm3 3D APT reconstruction showing the p-In0.01Ga0.99As, n-In0.05Ga0.95As and the GaAs layers. 4%, 100%, 0.1% and 0.1% of the indium, germanium, gallium and arsenic detected atoms, respectively, are shown. (b) 140x140x250 nm3 sampling volume extracted in the GaAs layer and the n-In0.05Ga0.95As layer in (a) showing germanium atoms and their diffusion along the dislocation. 100% of the Ge atoms are shown. (c) 140x140x107 nm3 sampling volume extracted from the GaAs layer in (a) showing the diffusion of indium along two dislocations. 100% of the indium atoms are shown. 108x131mm (300 x 300 DPI)


Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 3. (a-d) Maximal projections along the APT tip showing enriched linear features corresponding to dislocations. For this, the maximum concentration values from a 2×2×2 nm3 interpolated grid is projected into the plane of display. The indium and germanium maps are shown in blue and red respectively. Angles are guides to the eye showing reasonable agreement between typical dislocations in III-V materials and the APT data. Sites A-C are used for proximity histogram measurements in Figure 4 and 5. (e) Approximate diagram of the geometry of the dislocation fusion reaction as interpreted from the APT data. 222x132mm (300 x 300 DPI)


Page 26 of 29

Page 27 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

Figure 4. (a) Indium composition measured along the dislocation in the GaAs layer. (b) Germanium composition measured along the dislocation in the In0.05Ga0.95As layer. (c) Indium composition across the In0.05Ga0.95As/GaAs interface measured along the dislocation and in the matrix (away from the dislocation). The solid line is a fit to diffusion in one dimension from a constant source. (d) Composition profiles in the vicinity of the dislocation in the In0.05Ga0.95As layer labeled A in Figure 3d. Values of distances above 0 correspond to the inside of the germanium-rich regions while values below 0 correspond to the outside. We see no evidence of indium segregation in this layer. (e) Lateral outdiffusion of germanium averaged over a 3 nm straight section of dislocation in the InGaAs layer. The concentration is normalized to that in the core (Ccore Ge). The solid line is a fit to an approximate solution to radial diffusion out of a cylindrical surface of constant composition Ccore Ge with a radius of 1 nm. (f) Indium and germanium composition profiles along the threading dislocation averaged over 13 nm thick slabs taken just above and below the In0.05Ga0.95As/GaAs interface. Germanium atoms in the GaAs layer are seen to be slightly displaced from the indium atoms. 159x135mm (300 x 300 DPI)


Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 5. (a) A 100x100x140 nm3 3D APT reconstruction of a tip prepared from a region without dislocations. 100% of the Germanium atoms are shown. (f) Germanium-rich clusters seen in a maximal projection. Respective composition profiles in the vicinity of three germanium rich clusters labeled Site B (c), Site C (d) and Site D (e) in Figure 3d and 5b. Values of distances above 0 correspond to the inside of the Germanium rich clusters while values below 0 correspond to the outside. 122x101mm (300 x 300 DPI)


Page 28 of 29

Page 29 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

Table of Coutents graphic 70x38mm (300 x 300 DPI)


Fast Diffusion and Segregation along Threading Dislocations in

Recommend Documents