nucleation-related defect-free gap/si(100) heteroepitaxy via...

Nucleation-related defect-free GaP/Si(100) heteroepitaxy via metal-organic chemicalvapor depositionT. J. Grassman, J. A. Carlin, B. Galiana, L.-M. Yang, F. Yang, M. J. Mills, and S. A. Ringel Citation: Applied Physics Letters 102, 142102 (2013); doi: 10.1063/1.4801498 View online: http://dx.doi.org/10.1063/1.4801498 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/102/14?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Dislocation reduction through nucleation and growth selectivity of metal-organic chemical vapor deposition GaN J. Appl. Phys. 113, 144908 (2013); 10.1063/1.4799600 Control and elimination of nucleation-related defects in GaP/Si(001) heteroepitaxy Appl. Phys. Lett. 94, 232106 (2009); 10.1063/1.3154548 Oxygen induced strain field homogenization in AlN nucleation layers and its impact on GaN grown by metalorganic vapor phase epitaxy on sapphire: An x-ray diffraction study J. Appl. Phys. 105, 033504 (2009); 10.1063/1.3074095 Ductile relaxation in cracked metal-organic chemical-vapor-deposition-grown AlGaN films on GaN J. Appl. Phys. 97, 123504 (2005); 10.1063/1.1929856 Comparative study of GaN and AlN nucleation layers and their role in growth of GaN on sapphire bymetalorganic chemical vapor deposition Appl. Phys. Lett. 77, 3391 (2000); 10.1063/1.1328091

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Nucleation-related defect-free GaP/Si(100) heteroepitaxy via metal-organicchemical vapor deposition

T. J. Grassman,1,2 J. A. Carlin,3 B. Galiana,3 L.-M. Yang,2 F. Yang,2 M. J. Mills,2

and S. A. Ringel1,31Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210, USA2Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210, USA3Institute for Materials Research, The Ohio State University, Columbus, Ohio 43210, USA

(Received 19 February 2013; accepted 28 March 2013; published online 8 April 2013)

GaP/Si heterostructures were grown by metal-organic chemical vapor deposition in which the

formation of all heterovalent nucleation-related defects (antiphase domains, stacking faults, and

microtwins) were fully and simultaneously suppressed, as observed via transmission electron

microscopy (TEM). This was achieved through a combination of intentional Si(100) substrate

misorientation, Si homoepitaxy prior to GaP growth, and GaP nucleation by Ga-initiated atomic

layer epitaxy. Unintentional (311) Si surface faceting due to biatomic step-bunching during Si

homoepitaxy was observed by atomic force microscopy and TEM and was found to also yield

defect-free GaP/Si interfaces. VC 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4801498]

The ability to grow high quality epitaxial GaP layers on

Si has been of interest for decades, largely due to the desire

to use a GaP/Si heterostructure, with its small but non-

negligible lattice constant mismatch (0.37% at 300 K), as a

method to achieve III-V/Si integration. Integration is of

interest as an enabling pathway for the production of high-

efficiency, monolithically integrated III-V/Si photovoltaics,

as well as Si-based photonics, optoelectronics, and high-

speed microelectronics, since a virtual GaP (on Si) substrate

would support subsequent metamorphic epitaxy based on

GaAsP and GaInP alloys. However, the integration of GaP

with Si is not trivial, and incompatibilities of intrinsic mate-

rials properties, such as lattice mismatch, interfacial hetero-

valency (polar/non-polar), thermal expansion mismatch, and

surface/interfacial chemistry, have provided substantial bar-

riers to success and a general inability to sufficiently sup-

press the resulting electrically active crystalline defects,

including anti-phase domains (APDs), stacking faults (SFs)

and microtwins (MTs), and dislocations.1,2

However, recent molecular beam epitaxy (MBE) based

work focusing on the application of surface and interface

chemistry knowledge to the careful control and design of the

Si substrate preparation and GaP nucleation has demon-

strated that these heterovalent nucleation related defects

(APDs, SFs, MTs) can indeed be simultaneously and entirely

suppressed, and nucleation-defect free GaP/Si has indeed

been achieved.3 For this, a combination of Si(100) substrate

vicinality and preparation to yield a pristine, biatomic step

reconstructed surface,4 well-controlled GaP nucleation via

migration enhanced epitaxy,5 and an overall consideration of

epitaxial film mechanics and heterovalent interface proper-

ties in epitaxial structure design was used to produce high-

quality heteroepitaxial GaP/Si layers capable of supporting

further III-V epitaxy for device applications, particularly

photovoltaics.6,7

Similarly, much recent progress has also been made via

metal-organic chemical vapor deposition (MOCVD) growth

methods for such GaP/Si heteroepitaxy, wherein an insightful

surface preparation procedure on nominally exact-oriented

Si(100) substrates, along with an atomic layer epitaxy (ALE)

nucleation approach, has been shown to yield GaP (and sub-

sequent high-quality Si-matched BGaP and GaNP) films free

of SF and MT defects, although with a relatively sparse popu-

lation of internally self-annihilating APD defects still

present.8,9

Nonetheless, III-V alloys that are lattice-matched to Si

are inadequate for use in most technological applications

where an integrated III-V/Si materials system would be de-

sirable. In many cases, such as where metamorphic (lattice-

mismatched) III-V epitaxy is needed to provide access to tar-

get materials, the integrated GaP/Si system is expected to

serve as a growth template or virtual substrate. However, the

existence of interfacial APD disorder is likely to inhibit

dislocation glide, preventing the efficient relaxation of the

misfit strain between the GaP and Si;10 any such interference

with interfacial dislocation glide will likely result in the

generation of excess dislocation density, which can be detri-

mental to ensuing integrated devices.

Here, GaP/Si(100) heterostructures grown by MOCVD

that are simultaneously devoid of SFs, MTs, and APDs are

reported. The approach is generally modeled after the authors’

previously developed MBE-based methodology.3 A similar

combination of intentional Si(100) substrate misorientation to

yield a biatomic surface step reconstruction, Si epitaxy prior to

GaP nucleation to provide a pristine growth surface, and the

use of a Ga-initiated ALE nucleation process was found to pro-

duce GaP films free of all nucleation-related defects (APDs,

SFs, MTs). Additionally, the Si epitaxy conditions used in this

work yielded unintentional step-bunching, leading to the

formation of (311) surface facets, which are also found to be

benign with respect to GaP nucleation.

All GaP and Si growth reported herein was performed in

a 3� 2 in. Aixtron MOCVD system with a close-coupledshowerhead (130 mm inject area diameter). Precursors used

for the associated growths were silane (SiH4), triethylgallium

(C6H15Ga, “TEGa”), and tert-butylphosphine (C4H11P,“TBP”). The typical working pressure for all growth modes

reported here was 150 millibars. In-situ monitoring of the

0003-6951/2013/102(14)/142102/4/$30.00 VC 2013 AIP Publishing LLC102, 142102-1

APPLIED PHYSICS LETTERS 102, 142102 (2013)


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growths was performed via reflectance/pyrometry, while

post-growth analysis included atomic force microscopy

(AFM), high-resolution triple-axis X-ray diffractometry

(XRD), transmission electron microscopy (TEM), and scan-

ning transmission electron microscopy (STEM).

A variety of (100)-oriented Si substrates were used for

the growths described herein, including wafers with

50.8 mm and 76.2 mm diameters and intentional offcuts of

4� and 6� in the [011] direction, all with equivalent results.Prior to loading into the reactor, the substrates were etched

in a 1:100 HF:DI H2O solution to remove the native oxide

and provide a H-passivated surface. As in the authors’ previ-

ous MBE-based GaP/Si work,3 a thin (�90 nm here) Sihomoepitaxial cap layer was grown in-situ on the Si sub-strates at �760 �C, immediately prior to any III-V nuclea-tion, as a means to bury any persistent and likely

problematic, surface contaminants (particularly carbon); this

temperature is also sufficient to yield the biatomic step sur-

face reconstruction.4

Also following the previous MBE-based work,3 GaP

nucleation on the pristine Si surface was achieved via low-

temperature (450 �C) ALE. Low-temperature reactive TEGaand TBP precursors were used for the ALE nucleation, with

the TEGa pulses carefully calibrated (via AFM) to give exactly

full monolayer coverage. To prevent adverse Si-P reactions,

the ALE GaP nucleation was Ga-initiated.3 Following each

TEGa dose and purge, the surface was exposed to a flow of

TBP, followed by a purge and short pause to allow for reaction

equilibration. A total of 25 GaP ALE cycles was used for the

growths reported here. After ALE-GaP nucleation, the sub-

strate temperature was increased under TBP flow to �580 �C,where a 250 nm thick, but otherwise unoptimized, homoepitax-

ial GaP cap layer was grown via standard MOCVD process to

provide a film with sufficient bulk cohesion to survive subse-

quent high-temperature exposure, thereby producing a true

GaP/Si virtual substrate.

Figure 1(a) presents AFM scans of a homoepitaxial

(�90 nm) Si surface on a 6� offcut Si(100) substrate (with noGaP growth). Evident on the Si surface is a quasi-periodic

“ripple” structure, with vertical and lateral length scales

larger than expected for biatomic stepping on a vicinal sub-

strate, suggesting some sort of step bunching; the surface

appears, otherwise, to be atomically smooth, with a maxi-

mum calculated root-mean-square (RMS) roughness (from a

500� 500 nm2 image to somewhat minimize the effect of theripple) of 0.39 nm, equal to that of the pre-epitaxy Si surface.

Indeed, cross-sectional TEM/STEM (X-TEM/STEM) analy-

sis of such structures capped with subsequent GaP growth

(shown in Figure 2 for a similar 6� offcut substrate) reveal theexistence of tall (�4 nm), step-like structures with wide(�50 nm), flat terraces. The smooth step sidewall faces arefound to lie at an angle of about 25� from the (100) surface,consistent with the formation of (311) facets via biatomic

step bunching, as reported elsewhere.11,12 These (311) facets

are the result of anisotropies in the Si adatom surface and step

edge diffusion kinetics and are found to manifest under cer-

tain combinations of growth and/or annealing conditions

(temperature, growth rate, substrate misorientation).13,14 For

the sake of simplicity, and because results obtained from

4� offcut substrates were effectively identical to those from

6� offcut, with only slight differences in step periodicity andheight, only 6� offcut results are presented.

Fig. 1(b) presents an AFM scan of a GaP nucleation

layer grown by ALE on a 6� offcut Si(100) substrate identi-cal to that shown in Fig. 1(a). The image indicates a smooth

(0.60 nm RMS surface roughness), continuous film with no

Volmer-Weber type island formation15 and which maintains

much of the underlying Si ripple structure. Fig. 1(c) presents

AFM data from a 250 nm thick GaP layer grown via low-

temperature (580 �C) MOCVD on the ALE-grown GaP/Sinucleation layer. These as-grown films present flat and

FIG. 1. Atomic force microscopy images of the surfaces of (a) homoepitax-

ial Si (90 nm thick), (b) ALE-grown heterovalent nucleation layer, and (c)

as-grown heteroepitaxial GaP (250 nm total GaP thickness) surfaces grown

on Si(100) substrates misoriented 6� toward [011].

142102-2 Grassman et al. Appl. Phys. Lett. 102, 142102 (2013)


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relatively smooth surfaces, with typical RMS surface rough-

ness less than 1.0 nm (e.g., 0.87 nm for the 20� 20 lm2 imagein Fig. 1(c)) and no evidence of large-scale APDs.16 A few

dark spots can be seen in the image due to the presence of

small surface voids (�5 nm deep by AFM), most likely due tothe lack of optimization of the growth conditions and layer

thickness of the low-temperature MOCVD GaP cap layer;

such features are neither observed on the post-ALE GaP sur-

face (Fig. 1(b)) nor after subsequent high-temperature (725 �C)GaP MOCVD growth (not shown here)17 and are thus unre-

lated to the GaP/Si interface.

Figure 2 presents X-(S)TEM micrographs, at a range of

magnifications, from an example 6� offcut GaP/Si(100)sample prepared in the methods described above. Multiple

samples were imaged via both TEM and STEM in zone-axis

and two-beam g(200) and g(220) [not shown] conditions to

provide a thorough analysis of the heterovalent interface. As

displayed in Fig. 2(a), and effectively identical to the results

obtained previously via MBE,3 the only defects evident in

any such sample were the expected misfit/threading disloca-

tions due to growing beyond the critical thickness (approxi-

mately 40–90 nm at growth temp),18 indicating that the

heteroepitaxial nucleation and growth process used was

indeed successful at fully preventing the formation of all

nucleation related defects, including SFs, MTs, and even

small-scale APDs. However, not observed in the MBE work

are the periodic, large-scale step features that can clearly be

seen via zone-axis STEM imaging, such as in Fig. 2(b);

high-resolution STEM imaging of these steps, provided in

Fig. 2(c), shows the 25� inclined (311) step-edge faceting.While the (311) faceted step-bunching was an unin-

tended result of the epitaxial Si growth conditions used for

this work, its presence, and any potential impact (or lack

thereof) on the GaP/Si heterovalent interface, is nonetheless

interesting and worth consideration. Because the (311) facet-

ing is formed via the bunching of biatomic steps, the result-

ing large-scale steps would be expected to possess an even

number of atomic layers (i.e., hstep¼ 2n � aSi/4), a necessityfor the preclusion of APD nucleation due to shifted III-V lat-

tice registry. As such, STEM image based measurements

reveal even-numbered step heights on all such faceted steps

measured, with a median value of 8aSi on the 6� samples.

However, slope (i.e., height/width) analysis of the faceted

steps indicates that, in the case of the 6� offcut samples, only�3.8� worth of misorientation is actually accounted for bythe large-scale steps, suggesting that the wide terraces them-

selves still possess �2.2� worth of misorientation, which isstill sufficient to ensure full biatomic stepping to prevent

APD nucleation.19

Of particular interest is the GaP/Si interface at the (311)

facets. Since there are no observable nucleation-related

defects (APDs, SFs, MTs) at these facets, they must be con-

sidered benign with respect to the heterovalent nucleation.

Indeed, the atomic configuration of the Si(311) surface, with

alternating rows of 2- and 3-fold coordinated Si surface

atoms (i.e., with two and one dangling bonds, respectively,

as depicted in Figure 3),20 should yield a site-selective chem-

istry conducive to APD-free heterovalent epitaxy at these

facets, consistent with growth on Si(211) and Si(311) surfa-

ces as previously reported.15,21 Therefore, the serendipitous

combination of both biatomic stepping and (311) faceting on

the vicinal Si(100) surface, which on their own should be

sufficient for the prevention of APDs, appears to work in a

complementary (or at least non-conflicting) manner, ena-

bling the growth of GaP on Si(100) free of all nucleation-

related defects.

The results presented herein demonstrate the growth, by

MOCVD, of GaP on Si(100), free of all heterovalent

nucleation-related defects, including APDs, SFs, and MTs.

The same surface science guided approach previously dem-

onstrated via MBE for the suppression of nucleation-related

defects3—the combination of substrate vicinality, pristine

surface preparation by homoepitaxial Si epitaxy, and

Ga-initiated ALE nucleation—was shown to be equally

FIG. 2. Cross-sectional (scanning) transmission electron micrographs of a

nucleation-related defect-free heteroepitaxial GaP/Si sample grown

by MOCVD on a 6�-[011] misoriented Si(100) substrate: (a) bright-fieldtwo-beam g(200) TEM, (b) bright-field ½0�11� zone-axis STEM, (c) andatomic-resolution ½0�11� zone-axis high angle annular dark field STEM, not-ing the 25� angle of inclination of the (311) step-bunch facet from the (100)surface (155� declination from the associated terrace top).



169.228.173.121 On: Wed, 29 Oct 2014 02:45:21

effective for MOCVD-based growth. A particularly interest-

ing aspect of the MOCVD-based growths not seen in the

MBE-based work was the formation of (311) faceted step-

bunches which were found to yield defect-free GaP/Si

interfaces, providing an unanticipated simultaneous demon-

stration of an alternative heterovalent integration mecha-

nism. This work represents a critical validation of

methodology transition between the MBE and MOCVD

growth techniques, providing a pathway for the production

of heteroepitaxially integrated III-V/Si structures, with

applicability toward a range of important device technolo-

gies, via standard commercial fabrication approaches.

This work was fully or partially supported by Department

of Energy under the FPACE program (DE-EE0005398), Army

Research Office (DAAD 19-01-0588), and the Ohio Office of

Technology Investments’ Third Frontier program.

1V. Narayanan, S. Mahajan, K. J. Bachmann, V. Woods, and N. Dietz,

Philos. Mag. A 82(4), 685 (2002).2V. Narayanan, S. Mahajan, K. J. Bachmann, V. Woods, and N. Dietz, Acta

Mater. 50(6), 1275 (2002).3T. J. Grassman, M. R. Brenner, S. Rajagopalan, R. Unocic, R. Dehoff, M.

Mills, H. Fraser, and S. A. Ringel, Appl. Phys. Lett. 94(23), 232106(2009).

4D. J. Chadi, Phys. Rev. Lett. 59(15), 1691 (1987).5Y. Takagi, H. Yonezu, K. Samonji, T. Tsuji, and N. Ohshima, J. Cryst.

Growth 187(1), 42 (1998).6T. J. Grassman, M. R. Brenner, M. Gonzalez, A. M. Carlin, R. R. Unocic,

R. R. Dehoff, M. J. Mills, and S. A. Ringel, IEEE Trans. Electron Devices

57(12), 3361 (2010).7T. J. Grassman, A. M. Carlin, K. Swaminathan, C. Ratcliff, J. Grandal,

L.-M. Yang, M. J. Mills, and S. A. Ringel, in 37th IEEE PhotovoltiacSpecialists Conf. (2011), p. 003375.

8S. Liebich, M. Zimprich, A. Beyer, C. Lange, D. J. Franzbach, S.

Chatterjee, N. Hossain, S. J. Sweeney, K. Volz, B. Kunert, and W. Stolz,

Appl. Phys. Lett. 99(7), 071109 (2011).9K. Volz, A. Beyer, W. Witte, J. Ohlmann, I. N�emeth, B. Kunert, and W.Stolz, J. Cryst. Growth 315(1), 37 (2011).

10E. Kvam, J. Electron. Mater. 23(10), 1021 (1994).11A. Oshiyama, Phys. Rev. Lett. 74(1), 130 (1995).12W. Weiss, D. Schmeisser, and W. G€opel, Phys. Rev. Lett. 60(13), 1326

(1988).13J. Mysliveček, C. Schelling, F. Sch€affler, G. Springholz, P. �Smilauer,

J. Krug, and B. Voigtl€ander, Surf. Sci. 520(3), 193 (2002).14A. Pascale, I. Berbezier, A. Ronda, A. Videcoq, and A. Pimpinelli, Appl.

Phys. Lett. 89(10), 104108 (2006).15V. Narayanan, S. Mahajan, N. Sukidi, K. J. Bachmann, V. Woods, and N.

Dietz, Philos. Mag. A 80(3), 555 (2000).16Q. Xu, J. W. P. Hsu, S. M. Ting, E. A. Fitzgerald, R. M. Sieg, and S. A.

Ringel, J. Electron. Mater. 27(9), 1010 (1998).17C. Ratcliff, T. J. Grassman, J. A. Carlin, and S. A. Ringel, Appl. Phys.

Lett. 99, 141905 (2011).18Y. Takagi, Y. Furukawa, A. Wakahara, and H. Kan, J. Appl. Phys. 107(6),

063506 (2010).19O. L. Alerhand, A. N. Berker, J. D. Joannopoulos, D. Vanderbilt, R. J.

Hamers, and J. E. Demuth, Phys. Rev. Lett. 64(20), 2406 (1990).20D. J. Chadi, Phys. Rev. B 29(2), 785 (1984).21H. Kroemer, J. Cryst. Growth 81(1-4), 193 (1987).

FIG. 3. Atomic structures and GaP/Si interfacial bonding configurations at

the (a) Si(311) and (b) Si(211) surface/interface planes. Si dangling bonds,

and thus subsequent GaP/Si interfacial bonds, are indicated by the open

ovals.



169.228.173.121 On: Wed, 29 Oct 2014 02:45:21
http://dx.doi.org/10.1080/01418610208243196http://dx.doi.org/10.1016/S1359-6454(01)00408-6http://dx.doi.org/10.1016/S1359-6454(01)00408-6http://dx.doi.org/10.1063/1.3154548http://dx.doi.org/10.1103/PhysRevLett.59.1691http://dx.doi.org/10.1016/S0022-0248(97)00862-2http://dx.doi.org/10.1016/S0022-0248(97)00862-2http://dx.doi.org/10.1109/TED.2010.2082310http://dx.doi.org/10.1063/1.3624927http://dx.doi.org/10.1016/j.jcrysgro.2010.10.036http://dx.doi.org/10.1007/BF02650370http://dx.doi.org/10.1103/PhysRevLett.74.130http://dx.doi.org/10.1103/PhysRevLett.60.1326http://dx.doi.org/10.1016/S0039-6028(02)02273-2http://dx.doi.org/10.1063/1.2345223http://dx.doi.org/10.1063/1.2345223http://dx.doi.org/10.1080/01418610008212068http://dx.doi.org/10.1007/s11664-998-0154-8http://dx.doi.org/10.1063/1.3644956http://dx.doi.org/10.1063/1.3644956http://dx.doi.org/10.1063/1.3310479http://dx.doi.org/10.1103/PhysRevLett.64.2406http://dx.doi.org/10.1103/PhysRevB.29.785http://dx.doi.org/10.1016/0022-0248(87)90391-5

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